341 . 1—92EV—9625

341.1 92EU

Tampereen teknillinen korkeakouluVesi- Ja ympâristöteknhikan laltos

Tampere University of TechnologyInstitute of Water and Environmental Engineering

No. B 49

Ramadhani, M.

Evaluation of Vingunguti waste stabilization pondstreating municipal and industrial wastewaters

UDK 628.357 + 628.54ISBN 951-721-863-XISSN 0784-655X

LIBRARY, INTERNATIONAL REFEREF~’CECENTRE FOR COMMkJF.ITY WAl ER SUPPLYAND SAN~ÎATION(IRC)RO. Box 93190, 2509 AD The HagusTel. (070) 814911 ext. 1411142

RN:LO: 3(~1/. 1

Tampere, Finland 1992

t

1

EVALUATION OF VINGUNGUTI WASTE STABILIZATION PONDSTREATING MLJNICIPAL AND INDUSTRIAL WASTEWATERS

by Ramadhani Mussa

Page

TABLE OF CONTENTS 1

ABSTRACT 3

INTRODUCTION 51 . 1 General 51.2 Objectives of the study 51.3 Methodology and scope 6

2 WASTE STABILI2ATION PONDS 72.1 Features and processes of waste stabilization

ponds 72.1.1 Anaerobic ponds 72.1.2 Facultative ponds 102.1.3 Maturation ponds 122.1.4 Pond combinations 13

2.2 Design principles 132.2.1 Design of anaerobic ponds 132.2.2 Design of facultative ponds 152.2.3 Design of maturation ponds 17

2.3 Factors affecting operation of wastestabilization ponds 182.3.1 Climatic factors 182.3.2 Physical factors 202.3.3 Chemical factors 212.3.4 Wastewater flow and composition 222.3.5 Characteristics of receiving waters 22

2.4 Operational problems of waste stabilizationponds 22

3 COMBINEDMUNICIPAL AND INDUSTRIAL WASTEWATERTREATMENTIN WASTE STABILIZATION PONDS 243.1 Characteristics of wastewater 24

3.1.1 Dc)mestic wastewater characteristics 243.1.2 Industrial wastewater characteristics 253. 1 . 3 Characteristics of combined wastewater 29

3.2 Advantages of combined wastewater treatment 303.3 Limiting substances in combined wastewater

treatment 313.4 Need of pretreatment 32

4 VINGUNGUTI WASTE STABILIZATION PONDS 344.1 Background and location 344.2 Physical layout 354.3 Design criteria used 364.4 General observations 37

5 SAMPLING, ANALYSIS AND DISCUSSION OF RESULTS 425.1 Sampling and analysis 425.2 Results and discussion 44

5.2.1 Report on truck emptiers andguestionnaires 44

2

5.2.2 Biochemical oxygen demand 475.2.3 Fecal coliforms and fecal streptococci 505.2.4 Total dissolved solids 525.2.5 Anunonia, nitrate and nitrite 535.2.6 Heavy metals 545.2.7 Dissolved oxygen, temperature and pH 545.2.8 Flow measurement 565.2.9 Applicability of design equations 59

6 CONCLUSIONSAND RECOMMENDATIONS 616.1 Conciusions 616.2 Reconunendations 62

7 REFERENCES 64

APPENDICES 68

3

Ramadhani, M. 1992.Evaluation of Vingunguti waste stabilization pondstreating municipal and industrial wastewaters. TampereUniversity of Technology, Institute of Water andEnvironmental Engineering. Publication B 49. 77 p.

ABSTRACT

This work is mainly based on the field and laboratoryinvestigations done at Vingunguti waste stabilizationponds in Dar es Salaain, Tanzania. The ponds are treatingdomestic and industrial wastewater jointly. They consistof two anaerobic ponds in parallel, one facultative pondand three maturation ponds in series.

Details of the concerned industries were collected throughquestionnaires. Samples were collected twice per week frominlets and outlets of each pond unit during 11.11.1991 -

16.1.1992. The laboratory analyses inciuded tests forbiochemical oxygen demand (BOD5), total dissolved solids(TDS), fecal coliforms (FC), fecal streptococci (FS),anunonia (NH3-N), nitrate (N03-N), nitrite (N02-N), pH,copper (Cu) and chromium (Cr). These analyses were carriedout at the water section laboratory of the Faculty ofEngineering at University of Dar es Salaam.

More than 20 indlustries discharge their wastewaters intoVingunguti wast.e stabilization ponds. They inciudetextile, printing paints, metal and chemical industriesproducing heavy metals and other toxicants that inhibitmicrobiological growth in ponds.

The total performance of the Vingunguti wastestabilization ponds was poor. Total removal efficiencieson BOD5, TDS, I~rH3-N, N03-N and N02-N were 48 %, 44 %,19 %, 20 % and 51 % respectively. The total efficienciesin FC and FS reduction were 98.79 % and 98.83 %respectively.

The performance of the anaerobic ponds was the lowest,with BOD5 reduction of only 7 %. NH~-Nwas increasing by3 % in the ponds and N03-N and N02-N removal was only 7 %and 17 % respectively. The poor performance of theanaerobic ponds may be due to sludge accumulation, short-circuiting or presence of illegally discharged industrialtoxicants.

The facultative pond showed a slightly better performance.BOD5 removal was 39 % and removals of NH3-N, N03-N andN02-N were 4 %, 17 % and 47 % respectively. As thefacultative pond is directly receiving industria].effluents, the low performance may be attributed to theadverse effect of the industrial toxicants. Highestreduction in FC and FS was observed in the facultativepond: 93 % removal of FC and 85 % removal of FS.

4

The maturation pond~ were efficient in pathogenic removalonly. Individual removal efficiencies in the threematuration ponds ranged 57 - 77 % for FC and 66 - 75 % forFS.

The treatment efficiency of the Vingunguti wastestabilization ponds may be revived by rearranging theorder of flow in the ponds: all the wastewater (domesticand industrial) to flow first into anaerobic ponds, theninto facultative pond and finally into maturation ponds.Pretreating industrial effluents at their source may alsoimprove the situation.

5

1 INTRODUCTION

1 .1 General

Treatment of wastewater is necessary to prepare it forsafe, hygienic, nuisance free and environmentally sounddischarge onto :irrigated land surfaces or into receivingwaters such as r:Lvers, lakes and oceans.

Waste stabilization pond system is frequently thepreferred wastewater treatment method particularly intropical areas where the climate is favourable forbiological trealbment. High temperatures, intense solarradiation, long day-light hours and availability of low-cost land are the major factors that have made wastestabilization ponds to be used successfully in the tropics(Egbuniwe 1982). However, due to the complexity of theinteractions of the treatment mechanisms in the ponds, theexisting’ design methods have not been able to take intoaccount all the factors influencing their operation.

Joint treatmerit of municipal and industrial wastewaters inwaste stabilization ponds is increasingly regarded asenvironinentally and economically best way of handling thewastewater probiem. Industries discharge an enormousvariety of waste materials. Many industries produce toxicor non-biodegradable wastewaters while others producereadily biodegradable effluents that do not cause problemsduring treatment. Therefore, investigations on thebehaviour of waste stabilization ponds treating combinedmunicipal and industrial wastewaters are important forfurther improvement of the design methods and operationalprocedures.

1 .2 Objectives of the study

The main objectives of this study were:

1) to assess the efficiency of Vingunguti wastestabilization pond system as a whole and theefficiency of the individual pond units

2) to study the effects of the various industrialeffluents di.scharged into the ponds and recommendappropriate measures to be taken

3) to study the applicability of the design equationswith the actual conditions

4) to give recommendations for future improvement ofwaste stabilization ponds treating combined domesticand industrial wastewaters.

6

1 .3 Methodology and scope

The following approach was adopted during the thesisstudy:

1) Reviewing of available literature in journals,magazines, periodicals, research reports, text booksand other relevant publications.

2) Collecting data and information from the Ministry ofWater, Energy and Minerals, Dar es Salaam Sewerage andSanitation Department, Howard Humphreys (Tanzania)Limited and management of various industriesconcerned. This included consultations and interviewswith the author~Lties involved.

3) Field research study at the Vingunguti wastestabilization pond site. The study involved wastewatersampling from established sampling points at inletsand outlets of every pond unit. The samples were thenanalyzed in the laboratory. Some on—site analyzes werealso done. Flow measurement was done by installingweirs at inlets and outlets of the ponds. Record ofthe number of trips made daily by truck emptiers waskept to enable estimation of loading into anaerobicponds. Questionnaires were sent to various industriesdischarging effluents into Vingunguti ponds, askingfor details on the different processes involved inproduction, quantity and quality of wastewaterdischarged and other relevant details.

7

2 WASTE STABILIZATION PONDS

Waste stabilization ponds are biological treatment unitsin which purification of the wastewater is done with thehelp of microorganisms. The types of microorganisms achivein the purification process are determined by thecomposition of the wastewater and the conditions presentin the treatment units.

2.1 Features and processes of waste stabilization ponds

Ponds are classified according to the nature of biologicalactivity taking place within them. In these terms,stabilization ponds are classified as anaerobic,facultative and maturation.

2.1 .1 Anaerobic ponds

These ponds are generally used for pre-clarification andare usually the first stage in a series of pond systemswhere heavily loaded wastewaters have to be treated (Karpeand Baumann 1980). Anaerobic ponds lack dissolved oxygenand the active microbial population comprises strictlyanaerobic micro—organisms with a few traces of facultativemicro-organisms. The organic material present in theinfluent is degraded by ferinentative process (Horan 1990).

Anperobic process

The anaerobic fe:rmentation process converts waste organicmaterials to methaneand carbon dioxide in the absence ofmolecular oxyg’en. Figure 1 shows a diagram of themetabolic steps involved in anaerobic digestion andinteraction between the micro—organisms.

1

1 HYD~OLYS1S

SIMPLE ~GANIC COMPOUNDS

(Si~çar..Aminoac~du • PeptId~)

Legend:

1 fermentative bacteria2 H2-producing acetogenic

bacteria3 H2-consuming acetogenic

or homoacetogenic bacteria4 C02-reducing methanogenic ________

bacteria5 acetoclastic methanogenic

bacteria.

Figure 1. Metabolic steps involved in anaerobic digestion(Novaes 1986).

COMPLEX O~GANICCOMPOUNOS(Coibe~ydrat.i.Proleki. • Up~ds)

1 ACIDOGEN~

LONG O4AJN FATTY ACIDS(PrcpIonot.. eUIy~oI.~Ste)

2 $ ACETOGEP&ESJS

[~bO. 1 ACETOGEPES5

METHANO~~?~...1.J1CH4 .COz

8

In the first stage the organic substrates are hydrolyzed,resulting in simpler compounds, through enzymes producedby fermentative bacteria. In the second stage,acidogenesis occurs with the formation of hydrogen,carbon dioxide, acetate and higher organic acids thanacetate due to the activities of fernientative bacteria.The end-products such as butyric acid are extremelymalodorous (Novaes 1986). The following reactions takeplace (Vigneswaran et al 1986):

C6H1206 + 2H20 -> 2CH3COOH(acetic) + 2CO2 + 4H2 (1)

During the third stage, acetogenesis occurs and theorganic acids produc:ed are converted into hydrogen, carbondioxide and acetat:e by the acetogenic bacteria. Inaddition, a part of the available hydrogen and carbondioxide is converted into acetate by the homoacetogenicbacteria (Novaes 1986). The following reaction takes place(Vigneswaran et al 1986):

C02 + 4H2 -> CH4 + 2H2O

The reaction during the conversion of acetimixture of carbon dioxide and methane bmethane bacteria is (Vigneswaran et al 1986

CH3COOH-> CH4 + C02

C6H1206 -> CH3CH2CH2COOH(butyric) + 2C02 + 2H2 (2)

C6H12O6 + 2H2 -> 2CH3CH2COOH(propionic) + 2H20 (3)

CH3CH2COOH(propionic) + 2H20 -> CH3COOH+ CO2 + 3H2 (4)

CH3CH2CH2COOH(butyric) + 2H2O -> 2CH3COOH 2H2 (5)

During the last stage, a group of methanoboth reduces the c:arbon dioxide and dec~acetate to form methane (Novaes 1986). Thecarbon dioxide to niethane by hydrogen-uti.bacteria takes place through the follo(Vigneswaran et al 1986):

;enic bacteria~rboxylates thereduction ofLizing methaneqing reaction

(6)

~ acid into a~‘ acetoclastic

(7)

less and whenibute to the~ODremoved in

methane gas.)r many years

The resulting gaseou.s end-products are odou~they escape to the atmosphere they cont:process of BOD removal. About 70 % of the 1an anaerobic pond will be in the form ofAnaerobic ponds can therefore operate fwithout desludging (Horan 1990).

9

Methanogens are very sensitive to changes in pH value andthey will only tolerate a pH of 6.2 - 8.0. 1f the rate atwhich volatile acids are produced exceeds the rate atwhich they are degraded by the methanogens, the pH willfail and the methanogens will be inhibited and ultimatelykilled. The growth rate of methanogens is thus thelimiting step and determines the maximum organic loadingto an anaerobic pond (Horan 1990).

Temperature can also af fect methanogens. Their activity isvery low below 10 °C, but increases rapidly as thetemperature inc:reases. Temperature is, therefore, animportant facto:r for the calculation of the organicloading rate.

The other process involved in anaerobic ponds issedimentation. This process provides an additionalmechanism for the removal of BOD in form of suspendedsolids. The sedimented solids will undergo rapid anaerobicdecomposition at the bottom of the pond. A well designedanaerobic pond can achieve up to a 60 % BOD-reductiondepending upon the temperature and retention time (Horan1990). Figure 2 shows the generalized curve for theremoval of BOD and pathogens in relation to retentiontime.

BOD- REMOVAL

IN °‘o

0

Figure 2. BOD removal in relation to temperature anddetention time (Karpe and Baumann 1980).

When the sedimented organic material is degraded, a largeamount of amnionia is released as ammonium. Due to lack ofoxygen, nitrification can not occur and this anunonium

100

80

60

o ~( MARA

• GLOYNA(22°C)

20

2 4 6 DETENTION TIME ~DA1

10

leaves the pond in the effluent. The effluent from ananaerobic pond often contains up to 20 % more ammoniunithan is present in the influent.

Of particular importance in anaerobic ponds is thebiological interconversions undergone by suiphur—containing compounds. The evolution of H2S, which resuitsfrom the anaerobic reduction of sulphate, is responsiblefor the odours associated with anaerobic ponds. Thereaction proceeds according to the following equation:

CH3COOH+ S042 + 3H~—> 2C0

2 + H2S + 2H20 (8)

This reaction is carried out by suiphate reducing bacteria

and H2S is the major end product (Horan 1990).

2.1.2 Facultative ponds

The major role of the facultative ponds is the removal ofBOD. The ponds are characterized by three zones. In theupper regions, near the water surface, aerobic conditionsprevail. At the bottom of the pond reduction occurs underanaerobic conditions. Between these two layers there is afacultative region, where a mixture of both reactions takeplace (Karpe and Baumann 1980).

Aerobic zone

The aerobic condit.ions at the surf ace of the pond aremainly due to the photosynthetic activity of the algaegrowing where nutrients and light are available. Like allplants, algae produce oxygen which is absorbed by theaerobic bacteria living in wastewater (Karpe and Baumann1980). The bacteria consume oxygen in respiration andmultiplication and, at the same time, they break downorganic matter present in the wastewater. As a by—productof their metabolism, they release carbon dioxide, nitrogenand phosphate compounds which serve the algae as nutrientsand as raw material for photosynthesis. Sonie of the oxygenis again used by the aerobic bacteria thus continuing thecycle (WHO 1987). The symbiosis between algae and bacteriais summarized in Figure 3.

11

NEW CELLS

ORGANIC MATTER

4ALGAE

GACTER IA

4’

LIGHT

Figure 3. Symbiosis of algae and bacteria instabilization ponds (Karpe and Baumann 1980).

The photosynthesis process depends on the light intensity.The algae population decreases with the depth of the pondand the proportion of oxygen diminishes correspondingly.In the facultative zone of the pond, water contains littieoxygen and deeper in the anaerobic zone, it contains nooxygen.

Wind and heat are also determinants which control thefunction of the facultative ponds. Especially in thetropical zones, the upper water layer will heat uprapidly. Without the circulation of water caused by theactivity of wind, a discontinuity in temperature at adepth of only 50 cm can occur. Some of the algae may sinkdown from the warm water region (above 35 °C), forming alight barrier. This phenomenon will immediately cut downthe rate of photosynthesis and the production of oxygen.The pond will therefore “tip over” and become an anaerobicone (Karpe and Baumann 1980).

Anperobic zone

During the retention period of the wastewater infacultative ponds, all solid substances form sediment atthe bottom. Their anaerobic reduction takes place attemperatures above 15 °C, developing methane, carbondioxide, and other anaerobic gases. Anaerobic metabolismin the pond sediment serves to degrade sedimented sludgeand thus increases the times between desludging.Typically, desludging period for facultative ponds is5 - 10 years (Karpe and Baumann 1980).

c02

NEW CELLS

12

Facultative zone

This zone is characterized by all the processes takingplace in the aerobic and anaerobic zones. In addition,facultative bacteria consume combined oxygen from nitratesand sulphates when free oxygen is exhausted. Thestabilization process that takes place in a facultativepond is sununarized in Figure 4. The effluent of afacultative pond taken from the surf ace layer is stronglygreen coloured due to the presence of algae. It alsocontains other living organisms such as microcrustaceans,bacteria and rotifers, and has a high content of dissolvedoxygen. However, there are practically no suspended solidsthat will settle (WHO 1987).

WIND

SUNLIGHT

Figure 4. The stabilization process in a facultative pond(WHO 1987).

2.1 .3 Maturation ponds

Maturation ponds are used mainly for reduction ofpathogenic microorganisms such as viruses, bacteria andhelminths. This is achieved by providing a retention timelong enough (5 - 10 days) to reduce the nuniber to therequired level (Horan 1990). The bacterial effect ofmaturation ponds is due to several natural factorsincluding sedimentation, lack of food and nutrients, solarultra-violet radiation, high temperatures, high pH value,predators, toxins and antibiotics excreted by someorganisms, and natura]. die-of f (WHO 1987).

Suitably dimensioned maturation ponds reach a reduction ofcoliform bacteria of 99.99 % and a BOD-reduction of fromabout 60 mg/l to less than 25 mg/l. The ponds work undercompletely aerobic conditions and in general have a depthof 0.5 - 1.5 m (Karpe and Baumann 1980).

CH4

8

13

2.1.4 Pond combinations

The distribution of functions among the different pondtypes in a stabilization pond system means that two ormore types of ponds should be connected in series toachieve better effluent quality. Figure 5 shows thepossible pond arrangements in parallel and series.

al F1 8

Ii)

(iii)

1 ~EIJ~(v)

‘L~J LIJ 8L~II(v’i)

~)L~IH

~-~I~IH

(ix)

Legend: A = anaerobic pondF = facultative pondM = maturation pond.

Figure 5. Different arrangements of ponds (WHO 1987).

2.2 Design principles

2.2.1 Design of anaerobic ponds

To attain anaerobic conditions i.n the pond, the productionof oxygen by algal photosynthesis must be inhibited andthe rate of oxygen utilization must exceed the rate ofre-aeration at the surface. This is achieved by designingthe pond as deep as practically feasible (up to 5 m ormore) and ensuring a high organic loading rate (Horan1990).

There are various procedures used for the design ofanaerobic ponds, but all of them adopt one of thefollowing criteria:

- surface loading rate (kg BOD5/had)- volumetric loading rate (g BOD5/m

3d)- hydraulic retention time (d).

14

Surface lppding rate

For tropical regions, a pond is expected to be anaerobicall the time i.f surface loading is more than1 000 kg BOD5/had.

Surface loading is clefined as

= L~Q/10A (9)

where L5

QA

= surface i.oading (kg BOD5/had)= average i,nfluent BOD (mg O2/l~= average influent flow rate (m~/d)= surface area of pond (m

2).

However, according to Gloyna (1971) cited by WHO (1987),surface loading is inadequate for sizing an anaerobic ponddespite that it is still adopted by many designers.

Volumetric loading rate

The volumetric organic loading rate is defined as (Maraand Monte 1990):

= L~Q/V (10)

where Lv = volumetric organic loading rate (g/m3d)L~ = average influent BOD (mg O2/l~Q = average influent flow rate jm~/d)V = the required pond volume (mi).

The required value of Lv is selected on the basis ofmean temperature of the coldest month. Table 1 givesvolumetric design loadings for anaerobic ponds andcorresponding BOD

5 removals.

Table 1. Design loadings for BOD5 removals in anaerobicponds (Mara and Monte 1990).

Designtemperature°c

Volumetloadingg/m

3~d

ric BOD5 BOD5

remo%

va 1

< 10 100 4010 — 20 20T — 100 2T + 20> 20 300 60

T = design temperature

Retention time

Retention time is the most conunonly used design parameterin anaerobic ponds. Gloyna (1971) cited by WHO (1987) hasreconunendeda maximum retention time of 5 days in tropicalareas. The relationship between retention time and BODreduction is given in Table 2.

thethethe

15

Table 2. BOD reduction in anaerobic ponds as a functionof retention time (Mara 1976 cited by WHO 1987).

Retentiontimed

BOD5reduction%

1 502.5 605 70

Retention time is calculated as (Karpe and Baumann 1980):

t = AD/Q

where t retent:ion time (d)A = surface area of pond (m

2)D = depth of pond (m)Q = quantil:y of wastewater (m3/d).

2.2.2 Design of facultative ponds

(11)

A series of possible procedures for the calculation ofpond dimensions have been presented. The common empiricaland kinetic approaches are McGarry and Pescod equation,Gloyna equation and Marais and Shaw first order reactionequation.

McGarry and Pescod eguation

Surf ace loading is given by the following empiricalformula (Mara and Pearson 1987):

L50 = 60.3(1.099)T (12)

where L50 = the permissible surface loading (BOD5/had)T = meari air temperature (°C).

The equation has later been subjectedrefinements as follows:

Lso = 20T — 120Ls,o = 20T — 60Ls,o = lOT

= 50(1.072)T

to var±ous

All these equations give different loads for any giventemperature. Thi.s has led many designers to prefer akinetic approach (Mara and Pearson 1987).

Application of the McGarry and Pescod equatiori will resultin an effluent BOD5 of 50 - 70 mg/l (WHO 1987).

(13)(14)(15)(16)

16

Glpyna eguation

Gloyna’s empirical equation presumes a BOD removal of 80 -

90 % and has the following form (Gloyna 1976 cited byBanerji and Ruess 1987):

V = 3.5 X lO_5QLu(1.O8535_T)ff~ (17)

where V = pond volume (m3)Q = wastewater flow (l/d)Lu = ultimate influent BOD (mg/l)T = pond water temperature (°C)f = algal inhibition factor

= sulphide or other immediate COD factor.

Marpis and Shaw first order reaction eguation

This kinetic approach involves the following basicequation (WHO 1987):

Le 1(18)

L~ l+kTt

where Le = effluent: BOD5 (mg/l)

= influent: BOD5 (mg/l)kT breakdown rate at temperature T °C (d~)t = retention time (d).

The breakdown rate dLependson pond temperature:

kT = 0.3(i•05)T20 (19)

where T = pond operating temperature (°C).

From equation 19, th.e formula for the calculation of pondarea can be deduced as (Karpe and Baumann 1980):

Q(Li - Le)A= (20)

18D(1 05T—20)

where A = pond surface area jm2)

Q = wastewater flow (m~/d)D = pond depth (m).

The retention time (d) is given as (Karpe and Baumann

1980):

t = AD/Q (21)

The depth depends on the prevailing climatic conditionsand varies 1.0 - 3.0 m (Table 3).

17

Table 3. Depth of facultative ponds in relation toenvirorimental conditions and kind of sewage(modified from Karpe and Baumann 1980).

Recommendeddepthm

Environmentalconditions

Type ofwastewater

1,0 Uniform warmtemperature

Presettledwastewater

1,0 - 1,5 Uniform warmtemperature

Untreatedwastewater

1,5 — 2,0 Moderate seasonaltemperature fluctu-ations

Raw wastewatercontaining settle-able solids

2,0 - 3,0 Wide seasonal tem-perature variations

Large aniounts ofsettleable grit orsettleable solids

2.2.3 Design of maturation ponds

The removal of fecal coliform bacteria from any pondfollows a first order removal kinetics as follows (Horan1990):

Ne 1

1+kbt

where Ne = number of fecal coliforms in effluent= number of fecal coliforms in influent

kb = bacterial die-of f constant (d~~)t = retention time in pond (d).

(22)

Yanez (1982) cited by WHO(1987) has compiled data for thevalues of die-of f constant for fecal coliform bacteria andsalmonella (Table 4).

Table 4. Values of die-of f constant for differentbacterial species (modified from Yanez 1982cited by WHO 1987).

Organism kbd~

Temperature°C

Fecal coliforms 0.552 11-15Fecal coliforms 0.664 16—29Fecal coliforms 2.0 Not recordedFecal coliforms 2.6 20Salmonella 0.8 Not recorded

18

For a nuinber of ponds in series, the correspondingequation is (Horan 1990):

Me 1(23)

Ni (1 + kbta)(l + kbtf). . . .(1 + kbtm)n

where tal tf t:m = retention times of the anaerobic,facultative and maturation pondsin the series

n = the nuinber of maturation ponds required.

kb is sensitive to temperature and can be expressedas:

kb(T) = 2.6(l.07)(T_20) (24)

Solution of the design equation for maturation ponds is atrial and error procedure as equation (23) contains twounknowns: the number of ponds and the size that eachshould be. It is recommendedto have many small ponds thanfewer large ones with the same total retention time.However, careful decision on the the minimum size of pondis required to prevent significant short circuiting (Maraand Pearson 1987).

2.3 Factors affect.ing operation of waste stabilizationponds

There are several factors which may, advantageously oradversely, af fect the hydraulic and biological conditionsof wastewater stabilization ponds. Some of these factorscan be taken into account at the design stage whereasothers are beyond the designer’s and the operator’sinfluence. Care in site selection and design can reducethe impacts of some factors.

2.3.1 Climatic factors

Once a pond system bas been designed and constructed, itssubsequent performance relies largely on climatic factorssuch as wind action, temperature, rainf all, sunlight andevaporation (Lumbers and Andoh 1985).

Wind

Wind action is useful as it influences the mixing withinponds, thus minimizing short circuiting and ensuring areasonable uniform distribution of BOD, algae and oxygen.The depth of wind induced mixing in a pond depends largelyon the distance the wind is in contact with the water.Mara (1972) cited by Munene (1984), has indicated thatthis distance (unobstructed) should be about 100 m formaximum mixing.

19

To facilitate wind-induced mixing, the longest dimensionof the pond should lie in the direction of the prevailingwind. However, whenever possible, ponds must be siteddownwind of the community, in case odour problems arise(Horan 1990).

Temperature

Temperature is an important factor influencing theperformance of a waste stabilization pond. At highertemperatures, d:Lssolved oxygen present in the pond ispartly liberated to the atmosphere. At lower temperaturesit remains in the pond longer.

Temperature affects photosynthetic oxygen production aswell as other biological reactions. Optimum oxygenproduction for some species of algae is obtained at 20 °C,and limiting lower and upper values appear to be about4 °C and 37 °Crespectively (Gloyna 1971 cited by Mayo1988).

The function of anaerobic ponds depends also ontemperature. The right equilibriuni between the methane andacid-producing bacteria will only be achieved if the watertemperature is more than 1 5 °C (Karpe and Baumann 1980).

Rainf all

Rainfall will have some influence on pond performance andreliability. Ret:ention time in ponds is reduced duringperiods of rainfali. Heavy showers may dilute the contentsof shal].ow ponds, affecting the food available to thebiomass. On a very hot day, ram may cool the surfacelayer. The anaerobic sludge will then appear floating onthe surface and hence spoil the effluent. Simultaneously,the algal mats ori the surface of the pond will be drivento the bottom. Rainfall may also add oxygen to a pondthrough its own cLissolved oxygen and by increasing surfaceturbulence (WHO 1987).

Solar radiation

The intensity of solar radiation is an important factorfor the generation of oxygen through algal photosynthesis.Facultative ponds rely on solar radiation and theparaxneter varies mainly with latitude. Clouds also reducethe available light to some extent but direct sunlight isnot absolutely essential. The complex of 21 ponds at Lima,Peru, surveyed in 1979, is a dear evidence that s�abiliz-ation ponds can function without direct sunlight. A bluesky is rather uncommon there, yet the ponds have shown tobe operating under completely normal photosyntheticconditions (WHO 1987).

The bacterial mortality rate in ponds is also largelyinfluenced by th.e inactivation power of solar radiation(Mayo and Gondwe 1989).

20

Evaporptjon

Intense evaporation may upset the ecological balance instabilization ponds through the increase in theconcentration of solids. The salinity and theconcentration of organic matter may be increased to apoint at which the osmotic balance of the cells of theaquatic microorganisms is disturbed. It may also causeundesirable reductiLon in depth of water and af fectretention time. Evaporation rates up to 5 mm/d may beregarded as negliqible. However, in hot and regionsevaporation may exceed 15 mm/d (WHO 1987).

2.3.2 Physical factors

These factors are generally related to design andtherefore can be controlled.

Water depth

Stabilization ponds are normally operated at constantdepth. Intense seepage and evaporation or some emergencywithdrawal of pond contents may cause the water level todrop on occasions, c:ausing problems. 1f the depth drops toless than 0.6 m, aquatic plants are likely to grow veryquickly. A large part of the surface may become coveredwith weeds extending above the water level. As thepenetration of sunlight will be impaired, pond efficiencymay drop to an unacceptable level. In such a case,mosquito breeding ma.y also occur (WHO 1987).

Water depth requirements are different for every pond typesince the biological processes that take place in theponds are different.

Short-circuiting

Short circuiting in ponds is a cominon problem especiallyin the deeper anaerobic ponds. It results in stagnantzones within a pond which can cause odours. It alsoreduces the effective pond volume for wastewatertreatment. These effects can be minimized by proper choiceof pond geometry and proper placement of inlet and outletstructures.

For anaerobic ponds, a rectangular surf ace area isreconunended with a length to breadth ratio of less than3:1. Facultative and maturation ponds are designed toapproximate plug flow mixing, therefore higher length tobreadth ratios (up to 15:1) are employed. The inlet andoutlet structures should be placed at diagonally oppositecorners (Horan 1990).

Seepage

A survey on the ground permeability at a proposed pondsite is of great importance at the planning stage. Thiswill provide information regarding the need for bottomlining. Ponds built in permeable soils should be lined to

21

attain maximum d:Lscharge, especially if the effluent is tobe used for agricultural purposes. Lining is alsoimportant in cases where groundwater needs to be protectedfrom pollution (WHO 1987).

2.3.3 Chemical iEactors

The main chemical factors af fecting pond performance arepH, toxic materials and oxygen.

211

Both anaerobic and facultative ponds operate mostefficiently under slightly alkaline conditions. Mostorganisms in ponds have a pH tolerance of 6.0 - 9.0 andoptimum range of 7.0 - 8.0 (Abid 1983 cited by Mayo 1988).Methane fermental:ion in anaerobic ponds is af fected by pHchanges. Methanogens will only tolerate a pH range of6.2 - 8.0 (Horan 1990). Industrial wastewaters arenormally the causes for extremes of pH value in ponds. Itis therefore recommended that they should be controlled atthe source rather than introducing the complexity of pHadjustment at the influent to the ponds.

pH in the facultative ponds depends upon carbon dioxideconcentration in the medium. Due to the presence of excessC02 produced by aerobic bacterial respiration during thenight, pH value will be low in the morning hours. In theevening, pH value increases as a result of algae absorbingthe major part of the C02 in solution (WHO 1987).

Toxic materipis

The presence of t:oxic materials in industrial wastewatersaf fects the performance of waste stabilization ponds.Heavy metals, pesticides, detergents, wastes fromantibiotic—producing industries and many other industrialwastewaters that: inhibit biological treatment should becontrolled at the source (Alabaster et al 1991).

Oxygen

Dissolved oxygen is the best indicator of satisfactoryoperation of a facultative or maturation pond. In anormally functioriing facultative pond, super saturation offree dissolved oxygen at the surface and in the subsurfacelayers occur during the afternoon. The oxygenconcentration may drop to less than 1.0 mg/l at dawn dueto the presence of algae.

The aerobic surface layer prevents gases with odourproblems, released from the anaerobic layer, from comingout of the pond. However, odour problems still occur fromtime to time in facultative ponds due to the developmentof blue green algae when water temperatures are high.

22

Odour problems may also occur as a result of anaerobicpatches appearing on the surface of a pond when bottomtemperatures rise rapidly above 22 °C (WHO 1987).

2.3.4 Wastewater fiow and coinposition

Wastewater flow

Stabilization ponds are sometimes designed on the basis ofhydraulic retention time, a parameter directly related towastewater flow. In practice, the average flow rate isquite an adequate basis for design due to the relativelylarge volume of pond systems.

Wastewater compositi~

The design of stabilization ponds is directly related towastewater characteristics which are influenced by thetype of sewerage system and the contributing industries.Combined sewers convey a more dilute wastewater on rainydays whereas separate sewers are less sensitive torainfall. Infiltra.tion contributions, industrial andinstitutional discharges, dumping of septic tank sludgeinto the sewers and other circumstances of ten af fect thewastewater composition.

Organic loading, in terms of BOD5 or COD, is the mostfundamental parameter used in design. Some parametersother than organic loading may be important whereindustrial wastewaters are present in the sewage. Thesewill help the designer know if there is a need ofproviding pretreatment to protect the biomass in the pondsystem.

2.3.5 Characteristics of receiving waters

The pond effluent will either have to be disposed ofsomewhere (into a stream, lake, etc.) or is reclaimed forfurther use. The self-cleaning and dilution capacity of areceiving water under critical flow conditions should beknown to determine the degree of treatment to beprovided. Sometimes a heavily loaded primary pond may besufficient, while in other cases several ponds in seriesare necessary as a better effluent quality is essential.

2.4 Operational problems of waste stabilization ponds

Inspite of their relative operational simplicity, problemscan develop with stabilization pond systems which cancause a reduction in their efficiency, nuisance or damage.Many of the problems can be avoided or minimized by gooddesign and the rest can be preventec1 by maintaining goodoperational control and providing routine maintenance.Following are the common problems that occur instabilization ponds:

23

1) Development of algal scuni ori facultative andmaturation ponds: Algal mats may sometimes accumulateon the pond’s surface as a result of rapid growth ofblue green algae. The algal mats reduce lightpenetration •into the pond and they also produce odourproblems as they decay. The scum layer may be brokenup by means of water jets and It will sink to thebottom of the pond (Arthur 1983 and Munene 1984). Wang1991 noted that high concentration of algae ineffluents :Ls a typical problem in symbioticalgae/bacter:La systems of wastewater treatment. Theyof ten cause secondary pollution to receiving waterbodies.

2) High vegetal:ion growth on embankinents: Normally thepond embankments have a protective grass cover toprevent them from being eroded by wind and waveactions. However, when the grass is left to growuncontrolled, burrowing animals like moles and ratsmay invade the area and affect the safety of theembankments. Therefore the grass cover should alwaysbe cut short (Munene 1984).

3) Mosquito nu~Lsance: Mosquitoes create problems aroundwaste stabiJLization ponds. A poorly maintained pondwith a lot of growing weeds or scum provides abreeding sit:e for mosquitoes. Regular cleaning ofvegetation and removal of scum is necessary to controlinsects (Munene 1984).

4) Odour problems: Odour problems may arise from a numberof situations. Odours can be caused by the nature ofthe wastewat:er itself and also by the anaerobicconditions in the pond. Hydrogen sulphide, which isthe major compound produced by sulphur reducingbacteria, is responsible for odour problems in ponds.The best way to prevent the problem is to controlindustrial effluents. Another major source of odour isaminonia whic:h originates from the conversion of ureato carbon dioxide and ammonia (Henry and Gehr 1980).

5) Overloaded ponds causing poor effluent quality andodour nuisance. Al-Salem and Lumbers (1987) havereported a significant reduction in the efficiency ofAlsumra waste stabilization ponds in Jordan due tooverloading. The reduction of BOD through thefacultative ponds was found to be about 18 % only. Thepoor performance was attributed to the predominantlyanaerobic conditions observed in most of thefacultative ponds. The loading to the ponds wasgreater than that likely to lead to facultativebehaviour.

24

3 COMBINED MUNICIPAL AND INDUSTRIAL WASTEWATER TREATMENTIN WASTE STABILI~ATION PONDS

3.1 Characteristics of wastewater

The most frequently used characteristic parameters ofwastewater are (Pujol and Lienard 1990):

- Suspended solids (SS) and its organic fraction,volatile suspended sollds (VSS) whlch characterlze theparticular type of pollution.

- The chemical oxygen demand (COD) and the biochemica].oxygen demand in 5 days (BOD5) whlch guantify theorganic content of the wastewater. COD Indicates thetotal organic content while BOD5 indicates thebiodegradable orgranic content.

- Forms of nitrogen (N) and phosphorus (P). These arefertilizing elements whose dlscharges are llkely toaccelerate the eu.trophlc processes.

- The pH and condu,ctivity, which give a good indicationof the water ionicity.

- Fecal coliforms, which indicate the risk of infectionby pathogenic microorganisms.

- Heavy metals and inorganic salts, which indicateindustrial pollution.

3.1 .1 Domestic wastewater characteristics

The characteristics of domestic wastewaters are linked totheir origin. There are:

- sewage water from toilets which contains essentiallyorganic matter

- domestic wastewater from kitchens, bathrooms, etc. Thedaily discharge can vary considerably depending on theextent of the equipment and the hygienic habits such asshowers or baths. These wastewaters contain,principally, organic matter as well as householdproducts such as detergents and phosphates (Pujol andLienard 1990).

The characteristics of municipal wastewater depends onorlginal concentration in water supply, water usage andper capita consumption. Thus the characteristics vary fromone locality to an’Dther and even from season to seasonwithin the same locality (Yayehyirad 1984). The typicalcharacteristics of domestic wastewaters in smallcominunities are given in Table 5.

25

Table 5. Characteristics of domestic wastewater In smallcommun:Lties (Pujol and Lienard 1990).

Parameter Concentratlong/capita d

CODBOD5SSN—NH4~P—PO4

75—8030—3525—30

8—93.5—4

BOD5 and COD concentratlons confirm the organic nature ofthe domestic wastewater. The COD/BOD ratio, which Isslightly greater than 2, indlcates the biodegradablenature of such water (Pujol and Lienard 1990). Treatmentof municipal wastewater can, therefore, be easilyperformed in biological treatment units like stabilizatlonponds.

3.1 .2 IndustriaiL wastewater characteristics

Depending upon the processes involved in an industry,there is a wide variation in wastewater composition fromone type of industry to another. In this chapter,discussion is made on seven types of industries commonlyfound in Tanzania: textlle industry, tanning industry,food processing industry (fruit and vegetable canning),metal industry (pickling, plating and sheet milling),chemical industry, breweries and dairies. Selection ofthese Industries has taken into consideration therelevance of the discussion to the forthcoming chapters.

Textile industry wastewaters

Many substances present in textile effluents influenceCOD, some increasing it and others depressing it. Somesubstances will af fect BOD, suspended solids content andpH. Some organic compounds will be difficult to destroy bybiological oxidat:ion since they generally have a low BOD.These are said to be biologically hard. Those that arereadily oxidized are termed soft and usually have a highBOD. However, most of the organic compounds used in orextracted during textile processing are biodegradable tosome degree. In the absence of toxic materials, therefore,the blological process can be successfully used for thepurification of t:extile effluents (Yayehyirad 1984).

A typical example is from effluents of selected textileindustries in Tanzania. Textile mill operations inTanzania, generaily, consist of weaving, dyeing, printingand finishing. The wastewaters from the textile millscontain a variet:y of chemicals such as inorganic salts,organic acids, starch, hydrogen peroxide, detergentalkalis, urea and also waste products from a big number of

26

different dye—stuffs. Textile wastewaters are usuallycoloured, highly alkaline, contain high BOD and suspendedsolids and have high temperatures (Mashauri et al 1990).Table 6 shows the typical characteristics of textileeffluents.

Table 6. CharacterLstics of textile effluentsfrom Germirli et al 1990).

(modified

Parameter tinit Concentration

BOD mg/l 750TSSCOD

mg/lmg/l 2

240000

Colour mg Pt/.1 2 000pH - 6.9

Tannery wastewaters

The major sources of pollutants in tannery industry are(Gathuo 1984):

- the constituents of the raw hide which are necessarilyremoved or adapted during the leather making processincluding hair substances, various proteins and naturalfats of the hides together with any curing agents whichmay be utilized

- the chemicals employed in leather production, eitherpresent as surplus in their original form or convertedinto other products

- miscellaneous pollutants arising from housekeeping intannery, for example machine washing and other sanitaryactivities.

The cominon pollutants and their minimal amounts resultedin during the proctuction of chrome tanned leathers aregiven in Table 7.

Table 7. Tannery effluents characteristics (modified fromUNIDO/UNEP 1975 cited by Gathuo 1984).

Content Concentrationmg/ 1

BOD 800SS 650Chrome 43Suiphide 50N 136

27

As the raw material of the tanning industry is a naturalproduct, its soluble impurities are generally readilybiodegradable and represent a large part of the BOD badin the effluent. The process chemicals employed are avariety of inorganic and organic materials, affectingtotal solids, pH and COD. Of particular importance are theappreciable quan.tities of sulphide and chromium that arepresent. These substances have proved to have significanteffects on the performance of stabilization ponds(Yayehyirad 1984).

Fruit and vegetable canning industry wpstewater

Wastewater is normally generated during washing andrinsing, peeling, blanching and processing. Washing andrinsing is done to remove soil, microbial contamination,leaves or stems and to remove solubles and insolublesafter cutting, coring, peeling or blanching. Washing andrinsing operations constitute a major source ofwastewater. The volume of water used in these operationsmay be up to 50 % of the total usage (Gilde and Aly 1976).

Peeling operations produce wastewater containing largequanti�ies of suspended matter primarily organic innature. Blanching is done to expel gases from vegetables,to whiten beans and rice and precook them, to inactivateenzymes that cause undesirable flavour or colour changesin food and to prepare products for easy filling intocans. Little fresh water is added to the blanchingoperation, therefore the concentration of organicmaterials is high due to leaching out of sugars, starchesand other soluble materials from the product that isblanched. Although small in volume, wastewater fromblanching operation is usually highly concentrated withdissolved and colloidal organic matter (Gilde and Aly1976).

The final major sources of wastewater are from washingequipment, utencils and cookers. Also from washing offloors and general food preparation areas.

Metal industry w~stewater

The metal industries dealt with in this chapter aresecondary mills involved with finishing operations, suchas pickling, plating and sheet milling.

Pickling is a process of chemically removing oxides andscales from the surface of the steel. This is done usingwater solutions of inorganic acids such as sulphuric,hydrochloric, nitric and phosphoric acids. After pickling,the steel passes through rinse tanks. The sources ofwastewater from pickling operations are the strong spentacid solutions and the rinse water (Bramer 1976).

Metal plating consists of coating the finished metalproduct with a thin sheet of another metal for protectiveor decorative purposes. Processes in this operationinclude cleaning in alkaline solutions, rinsing, pickling,

28

melting, chemical treatment and oiling. Wastewatersgenerated in plating industries include rinse water andconcentrated process solutions. The metal content of theeffluent commonly includes tin, chromium, zinc, copper andnickel, cadmium, aluminium and iron (Longhurst and Turner1987).

In the sheet and strip mills, slabs are robled with acontinuous hot-strip mibl. The slabs are brought torolling temperature in continuous reheating furnaces. Theconditioned slabs are then passed through scabe breakersand high-pressure water sprays dislodge the boosenedscales. Cooling water is then sprayed and the finishedstrip is coiled. The sources of wastewater in the sheetand strip mill operation is the cooling water and thesprayed high pressure water (Bramer 1976).

Chemical industry wa.stewater

Most of the highby pollutional wastewaters from chemicalindustries originate from process areas. This includeswater formed or ebiminated during reactions, wash—watersfrom cleaning opera.tions, stem condensate from strippingoperations and accidental bosses due to spills andcarebess operation.

Process wastewaters may contain a variety of constituentsincluding a portion of the feed-stock chemicals, products,by-products, side products and spent catalysts. Acidic andalkaline discharges are the characteristics of mostchemical industries (Parsons 1976).

Brewery was tewater

The production of beer has two stages, mabting of barleyand brewing to beer from the mabt. Brewery wastes arecomposed mainly of liquor pressed from the wet gram,liquor from yeast recovery and washed water from thevarious departments (Arellano 1987).

The major componerits of brewery wastewater are BOD andsuspended solids which are produced in the brewhouse,during fermentation stage and during the bottling stage.The variations in brewing tradition and household practiceare refbected in the effluent BOD values which arenormally in the range of 0.8 - 2.5 kg/m3 (Henze 1983). Thetypical breweries wastewater production and compositionare given in Table 8.

29

Table 8. Charact.eristics of effluents from(modified from Henze 1983).

breweries

Content Concentrationmgr / 1

SS 1 500VSS 900Total BOD 1 500Soluble BOD 500Total COD 2 000Soluble COD 650Total N 30Total P 5

ppjry products wastewater

Processing and manufacturing of dairy products are waterintensive operations both during product preparation andmanufacturing. Maintenance of sanitation within theprocess area also uses a bot of water. This resuits in aproblem in treatment and disposal of the large volume ofwastewater generated. Dairy wastewaters contain phenolicsubstances which are supposed to be free from toxicsubstances. Phenols come from flavouring and from phenolsanitizing rubber boots used by workers in the processingarea. Other contents include BOD, SS, nitrogen sulphur,grease and oil (Table 9) (Diaz 1987).

Table 9. Dairy products1987).

wastewater characteristics (Diaz

Parameter Unit Averageconcentration

BOD5Suspended solids

mg/lmg/l

695215

Grease and oil mg/l 117pH 11Total solids mg/l 1 480Nitrogen mg/l 0.95Phosphates mg/l 0.11

3.1 .3 Character]Lstics of combined wastewater

Industrial wastewaters contain materials having a widerange of different characteristics. In most casesindustriab effluents are composed of toxic or non-biodegradable materials. However, it is not uncommon tofind industrial effluents that cbosely resemble domestic

30

sewage and are therefore suitable for biobogicaltreatment. Some inciustrial effbuents can be effectivebytreated by mixing with domestic sewage to improve thenutrient balance of the waste and to dibute the toxiccompounds present (Alabaster et al 1991).

Generally, industrial wastewaters may be:

— non—harniful at a].b to treatment -

— harmful to treatment processes- harmful to sludge utilization— useful to treatment processes

or a combination of the above when combined with municipalwastewaters.

3.2 Advantages of combined wastewater treatinent

The easiest and most effective way of dealing with tradeeffluents is to admix it with domestic sewage. However,there are limits to the type of effbuent which should beaccepted. For exainple, the discharge must not containsubstances which alcne or in combination will inhibit thebiological processes of biobogical treatment (Holding1990).

The performance of stabilization ponds which are treatinga mixture of domestic and industrial wastewaters can beput at risk by the presence of hazardous chemicals in theindustrial wastewater fraction. Effluents from foodprocessing indust,ries, which comprise readilybiodegradable organic matter are relativeby easy to treat.In contrast, heavy metabs from metal industries, such ascopper, zinc, nickel, lead, cadmium and chromium can reactwith the microbial enzymes to retard or completely inhibitmetabolism (Yayehyirad 1984).

Because of their comparatively long retention time,stabilization ponds albow a greater buffering capacityagainst shock loads of toxic inaterial and a longer periodfor the biobogically hard compounds discharged fromindustries. Other biological treatment systems such asactivated sludge and trickling filters have shorterretention times and hence back this advantage (Arthur1983).

High strength industrial wastewaters with BOD boading inthe range of 10 000 - 30 000 mg BOD/l can be treated byempboying anaerobic ponds as pretreatment units. However,anaerobic processes are susceptible to inhibition byexcess of subphide as hydrogen subphide. The sulphateloading rate should be kept below 500 mg SO4

2/m3 d (Maraand Pearson 1987).

Oib and grease from industries can be well trapped inanaerobic ponds that have subsurface effluent of f take. Theoil and grease are thus prevented from reachingfacultative ponds and are gradually degraded in theanaerobic ponds.

31

In the case of textile effluents, joint treatment withmunicipal sewage can be considered to be the bestalternative. By combined treatment, especiably if textilewastewaters form one quarter or less of the total volume,many difficulti.es are solved. Fbow, alkabinity andtemperature extremes and fbuctuations can always becorrected. Also decoboration is done more efficiently(Grau 1991).

Textibe effluents are normally deficient in nitrogen andphosphorus and therefore it becomes necessary to addnutrient materials, like ammonium subphate, to restore thebalance before any biologicab treatment is given. This iswhy It is preferabbe to treat these effbuents in admixturewith municipal sewage which will suppby the requirednitrogen and phosphorus (Yayehyirad 1984 and Grau 1991).

The soluble impurities from tanning industry are generalbyreadily biodegradable and therefore they can beeffectiveby and cheapby treated in waste stabilizationponds together with domestic sewage. The problem of highconcentration of chromium can be taken care of inanaerobic ponds and facultative ponds arranged in series.This has been proved by the performance of Nakuru wastestabilization pond system in Kenya. The averageconcentration of chromium in the raw sewage was found tobe 1.58 mg/b. Approximately, 20 % of this was removed inthe anaerobic ponds with a further 48 - 60 % removed inthe first facult:ative pond. The second facultative pondremoved a further 12 - 24 % and bevels were undetectablein the effluent:s from the third pond (Ababaster et al1991).

3.3 Limiting substances in combined wastewater treatment

Following is a JList of the common substances which couldcreate difficubties in biological treatment units. Thelist serves to illustrate the kind of probbems associatedwith treating industrial discharges together with domesticsewages (Holding 1990).

Acids and alkabi~: The optimum pH range for the biobogicaltreatment of sewage is around 6.5 — 8.0. Any acid oralkaline discharge which causes the pH of the mixed sewageto fall beyond the range will require neutrabizationbefore discharge

Non—ferrous metabs: Non—ferrous metals such as cadmium,chromiuin, copper lead, mercury, nickel and zinc, have aninhibiting effect on biological processes. When theirsludges are reused for agricuiturab purposes, they mayinhibit crop growth, be assimibated by the plant and enterthe food chain.

Oils and fats: These substances are a common occurrence inindustrial wastewaters. They can inhibit atmosphericoxygen which is vital for biologicab wastewater treatment.

32

Pesticides and detergents: These are non-biodegradablecompounds that can kill the bacteria present in the ponds.

5ulphate~ and sulphides: Excess of subphides as hydrogensulphide inhibit the anaerobic processes in ponds.

Additional problems occur 1f the industriab effbuentscontain substances with unknown environmenta].consequences.The damagemay be done before the potentialis even realized. For example local farmers used driedsewage sludge for soil conditioning until severe damagewas noticed on a crop of pyrethruin. When the sbudge wasanalyzed, trichlorobenzoic acid was discovered at aconcentration of jiust one part in 100 M, but stil]. asufficient amount to damage the crop (Holding 1990).

3.4 Need of pretreatinent

The most important objective of pretreating industriabeffbuents is to prevent problems in the sewerage systemand with any of treatment processes empboyed (Upstone1990).

Each industry is to some extent an individual case,therefore thorough study should be done to be able tocharacterize the effluents from a particular industry andpropose pretreatment possibilities. Thoroughinvestigations are important on the water balance, theprocesses involved, chemicals used, level of housekeepingand managementof water and wastewater for each industry(Rantala 1987).

Pretreating textile effluents

The presence of colour in textile wastewaters is a commonproblem. The dyes are, in general, biologically non-degradable or slowly degradable. These would consequentbylead to a very high turbidity in facultative ponds,limiting light penetration, and thus limiting algaegrowth. Inspite of the positive features of the combinedtreatment, in many cases the effluent is still coloured.It is practically impossible to estimate beforehanddecoboration effici.ency of joint treatment. Even pilotexperiments do not guarantee perfect prediction ofdecoloration. Permanent changes of palette, types of dyesand fibres introduce unpredictable stochasticity. Fbexiblepretreatment for textile effluents is thus a necessity(Grau 1991).

Pretreating tannery effluents

Tannery discharges have high sulphide content (up to40 mg/l). When these discharges pass through to thefacultative ponds they resubt in the inhibition ofphotosynthetic algae. The pond water frequently turnsbright pink due to profuse growth of purple photosyntheticbacteria which utilize sulphide. They convert the sulphide

33

to ebementabsulphur and deposit it within the cel].. Theprofuse growth of the sulphur bacteria resubts in a highturbidity in the ponds. Light penetration and hencephotosynthetic oxygen production is thus limited.

Ababaster et al (1991) have reported on the poorperformance of the stabibization pond system in Nakuru,Kenya due to high sulphide levels in the raw sewage. It isprobable that 1f the tanneries were to instalb apretreatment facility for sulphide recovery, then asufficient improvement in performance of the ponds wouldbe seen. Pretreatment is also required to reduce the highamount of chromiuzn present in tannery wastewater.

The common pretreatment activities inciude:

- Lowering the concentration of SS: This is a mechanicalpretreatment for capturing suspended solids such asshort fibres from a textibe industry.

— Grease and oil removab: Grease and cii are usuallylighter than water and may be separated by passing thewastewater through an interceptor or grease trap. Theinterceptor consists of a tank divided intocompartments in which the grease and oh fboat to thesurface of the wastewater and is retained by baffles.

- Cooling: Large volumes of hot industrial wastewatersmay be coobed using cooling towers or spray ponds.

- Neutralization: Wastes with bow pH value may becorrected by addition of an abkabi. Usually, there is achoice of alkalis, some of which may produce aprecipitate and hence require a subsequent settlingstage. The most common alkalis used are sodiumhydroxide and sodium carbonate. Highly alkalinewastewaters are neutrabized by inorganic acids such ashydrochboric (D~ sulphuric acid.

- Screening: This is designed to remove large fboatingand suspended sobids by passing wastewater throughracks or screens before it enters into a tretmentplant. Screens may take the form of bars, wires orperforated plates. Collecting the solids from thescreens can be done by mechanicalby operated rakes.Screening reduces the sobids boading on subsequenttreatment system. Sreening is particularby importantfor food processing and textibe industries (Gilde andAly 1976 and Diaz 1987).

- Grit removal: This is employed to remove smaller andmore dense solids like sand and cinders. Metalindustries and building construction firms normallyproduce this type of wastes. Grit removal may be donethrough channels and washing collections either by handor mechanically. Removedgrit is typical].y land filled(Diaz 1987).

34

4 VINGUNG(JTI WASTE STABILIZATION PONDS

4.1 Background and bocation

Vingunguti waste stabilization ponds are bocated in Ilabadistrict in Dar es Salaam region. They can be approachedby using Pugu road or Uhuru street from the Dar es Salaamcity centre. The ponds are about 12 km from the citycentre and about 200 m north-west of TAZARA (TanzaniaZambia Railway Authority) railway station (Figure 6).

The ponds started operation in 1976, a time during whichonly industriab wastewaters from Pugu Road industrial areawere treated. At the beginning there were only four ponds;the first being facultative and the remaining threematuration.

In 1986 rehabilitation work began due to poor performanceof the ponds wh±ch resulted from poor maintenance. Therehabilitation work consisted of constructing a dumpingstation (three chanibers) to receive domestic wastewaterfrom pit latrines and septic tanks carried by truckemptiers. Two anaerobic ponds were also added to treat thedomestic wastewater. These additional units started tooperate in February 1990.

Figure 6. Location map of Vingunguti waste stabilizationponds (Howard Humphreys 1988).

35

4.2 Physical bayout

Vingunguti waste stabilization ponds consist of six ponds:two anaerobic ponds (A1 and A2) in parallel, onefacultative pond (F) and three maturation ponds (M1, M2and M3) connected in series (Figure 7).

Figure 7. Layout plan of Vingunguti waste stabilizationponds (Howard Humphreys 1988).

Combined treatment of domestic and industrial wastewaterin the ponds begins at the first maturation pond. Thispond receives wastewater from facultative and anaerobicponds that receive industrial effluen�s and doxnesticsewage respectively. The firial effluent from the ponds isdischarged into Msimbazi River which fiows to the IndianOcean.

0

2

~8m

A1, A2FM1, ~

= anaerobicponds= facultative pond

!13 = maturation ponds.

36

According to Howard Humphreys (1988), the anaerobic pondshave been designed to treat domestic wastewater fromTemeke area which serves about 12 500 pit latrines and 600septic tanks. However, physical observations showed thattruck emptiers (Figure 8) collect wastewater (domestic)from other areas of the Dar es Salaam city too. They alsocollect industrial wastewater from some nearby industrieswhich have not been connected to any sewerage system.

A truck emptier discharging wastewater into achamber at Vingunguti waste stabilizationponds.

4.3 Design criteria used

This chapter gives a~ short description of the formubas anddesign criteria used for Vingunguti waste stabilizationponds. The design parameters used are given in Table 10.

Table 10. Design parameters used in the design ofVingunguti waste stabibization ponds (Howardand Humphreys 1988).

Parameter Unit Value

Influent flow to ponds A1Influent fbow to pond FInfluent flow to ponds M1,BOD5 bad in ponds A1 and

and

M2A2

A2

and M3

m3/d

m3/dm3/dg/ha.d

12017622002

50BOD5 reduction in ponds A

1Temperature

and A2 %OC

7025

Effluent BOD5Effluent FC

mg/lno./100 ml <

< 5437

-~

Figure 8.

37

For the design of the two anaerobic ponds, equation (11)was used:

t= 5dD= 3mBOD reduction = 70 %Q = 120 m3/d for each pond.

For the design of the facultative pond, equation (20) wasused:

A = pond area required (m2)Q = 1762 m3/d

= 400 mg/lLe = 60 mg/lD = 1.3 mT = 20 °C

For the design of maturation ponds, equation (22) was usedto check the bacteriological quality of the pond contents:

Ni 4 x 1O~FC counts/100 mlMe = 5 X i0~ FCkb = 3.1 d~t = 7 d/pond

Using the above design formulas and criteria, thegeometrical dimensions and hydraulic characteristics ofthe ponds were determined (Table 11).

Table 11. Dimensions of Vingunguti waste stabilizationponds (Howard and Humphreys 1988).

Pond Retentiontimed

Depth

m

Vol

m3

unie

A1 5.00 3.00 600

A2 5.00 3.00 600F 7.08 1.30 12 480M1 6.66 1.15 13 340M2 7.57 1.10 15 154M3 7.08 1.00 14 175

4.4 General observations

Observation during the study period showed that generallythe ponds were well taken care of by the attendants. Grasswas cut short regularly on the embankments and the pavingslabs on the banks of the ponds were all in place (Figure9). A few species of duck and other birds thrive in thelast two maturation ponds indicating that the water inthose pond units was cleaner than in the preceding ponds.

38

Figure 9. A view showing the facultative and maturationponds. The paving slabs on the embankments arewell in place and the grass has been cut short.

However, the folbowing negative aspects were noticed:

— Scum accumulated at the corners of the ponds especiallyanaerobic ponds which also possessed strong smells.Layers of thick mats were found in anaerobic pondswhich, however, were removed after some days (Figure10).

Figure 10. A view of the Vingunguti anaerobic pondsshowing the inlet pipe and scum accumulation.

39

- The usual blue/green cobour of the facultative pondwastewater d:isappearedin some days and no algae wasseen. This may be brought about by the toxicants fromthe industries which were boaded in the pondsperiodically. However, the normal condition of thefacultative pond water was restored after three to fourdays.

Some of the concrete channels making the outlets of theponds have deteriorated thus water was leaking throughthe embankmenlbs (Figure 11).

Figure 11.

- A considerably large portion of the fence that marksthe boundary of the pond site has been damaged and thenearby residents were always trespassing through.

- People have built houses adjacent to the pond site.This has made them victims of the nuisance from odourand mosquito breeding (Figure 12).

One of the cracked concrete channels atVingunguti waste stabilization ponds causingwastewater to by-pass the installed V-notchweir~.

40

Figure 12. A view showing the inlet pipe into theVingunguti facultative pond conveying indus-trial wastewater. Neighbouring residentiabhouses are adjacent to the ponds.

- There were no fbow measurement facilities at the inletsand outlets of the ponds. For regular monitoring of theponds, f 10w measurement is essentiab.

- The final effluent from the ponds was used for wateringnearby gardens before the rest was let to f 10w to theMsimbazi River. 1f the crops grown are consumeduncooked, a health hazard may occur.

— The raw industrial sewage was screened at the inlet tothe facultative pond but there was no oil separationfacility to remove grease and oil coming with theindustrial wastewater (Figure 13).

tS

t

- -

- -~

41

-r— t -~

-- —

- ‘t-

- ~Çr ~

v. aLs.

Figure 13. Screening facility at the inlet tofacultative pond at Vingunguti.

the

- The inlet pi]pes into anaerobic and facultative pondswere above the pond water level. This may be causingshort-circuiting.

—n — -,s.=- ~ ---t.~ -

-~‘-~.-—~. .-‘.——- ..._~_. —-— .r — -

T 4

t—’

42

5 SAMPLING, ANALYSIS AND DISCUSSION OF RESULTS

5.1 Sampling and analysis

Sainples were collected during eight weeks (NovemberJanuary 1992) between 9.00 am and 12.00 noon.samples were collected twice per week. Samples werefrom inlets and outlets of each pond unit toevaluation of the performance of each pond (Figure

Legend

= inlet for anaerobic ponds (domestic wastewater inlet)= outlet for anaerobic ponds= inlet for facultative pond (industrial wastewater inlet)= outlet for facultative pond= outlet for the first maturation pond= outlet for the second maturation pond= outlet for the last maturation pond

Figure 14. Sampling pointsstabilization ponds.

at Vingunguti waste

1991 --

Seventaken

enable14).

‘t

• k~_M~•_~~____lc._•_N_.__•__x

u

n—_ ~$—x~~—M —

AlAO1FM 1M1M2M2M30

43

Composite sampling is the recommendedsanipling techniquewhereby samples are collected at regular intervals andthen mixed in one large sample over a period of 24 hours.Throughout this study, however, grab sampbing has beenused due to time limitation and inadequacy of samplingbottles and other necessary facilities. Pearson et al(1987) reported that for the determination of pH and fecabcoliforms, grab samples are required.

Pearson et al (1987) also recommended two sampling periodsfor better evaluation of waste stabilization ponds; duringthe hottest and coldest seasons of the year. This was notpossible since the field study period was limited to sixmonths. Sampling for this study was done during thehottest period of the year (November - January).Therefore, the performance of the Vingunguti wastestabilization ponds can only be evaluated in thisparticular period and not in the extreme climate periods.

The parameters analysed in the laboratory were biobogicaloxygen demant (BOD5), total dissolved solids (TDS), fecalcoliforms (FC), fecal streptococci (FS), pH, ammonia,nitrite, nitrate, copper and chromium. Samples were notcollected from the industries for laboratory analysis.This was due to the big number of industries that wereinvolved, the Limitaion of time avaibabbe and inostimportant, the difficulty in testing heavy metals in thelaboratory. Only a few sainples from the Vingunguti wastestabilization ponds were tested for heavy metals duringthis study. Heavy metals and toxicants would have beenparameters of f:Lrst priority if wastewater samples fromthe individual industries were tested.

The analyses were carried out at the water sectionlaboratory of the Faculty of Engineering at University ofDar es Salaam. The paraineters analysed were selected afterconsidering the importance in waste stabilization ponds,the capacity of the laboratory and the time availabbe forthe study. All the parameters were analyzed according tothe standard methods for examination of water andwas tewater.

Unfiltered samp:Les were tested for BOD5. Analyzes weredone under standard conditions:the sample was stored forf ive days in the dark at 20 °C. In case analysis was notpossible immediately after sampling, samples were storedfor not more than 24 hours. Dissolved oxygen was measured,using dissolved oxygen meter, before and f ive days afterstoring the sample in the dark.

All samples for the bacteriological tests were collectedin steribized sampling bottles and tested immediately onarrival at the laboratory. The fecai coliform and thefecal streptococci bacteria were measured using thestandard membrane filter procedure according to thestandard methods.,

Ammonia, nitrite nitrate were measured using Lovibond rawwater test kit and TDS was measured by a HACH TDS-meter.pH was determineci by Orion pH-meter and heavy metals weretested using DR 200 Spectrophotometer. The on-site tests

44

included determination of dissolved oxygen andtemperature in the ponds using temperature/dissolvedoxygen meter type YS1 model 54A.

5.2 Results and discussion

In this chapter, presentation and discussion is made onthe records obtained of the truck emptiers visiting thesite daily and the information collected from theques�ionnaires sent to the various industries. The resultsof laboratory ana].yses and the resubts of the on-siteanalyses, including flow measurements, are also presentedand discussed. Appendix 1 shows the detailed resuits oflaboratory analyses and Appendix 2 Tanzanian temporarystandards for effluents.

5.2.1 Report on truck emptiers and guestionnaires

Truck emptiers

Table 12 shows the t:rips made weekly by the truck emptiersto Vingunguti waste stabilization ponds. Some difficultieswere faced during interviews with the truck operators: insome cases it was not possibie to obtain true informationon which area of the city or what industry the wastewaterhas been collected from.

Table 12. Truck emptiers discharging wastewaterVingungut.i waste stabilization(12.11.1991 — 11.1.1992).

trips per day = 26 Minimum no. of trips per day = 14

“ “ = 36 Percentageof domesticwaste-water brought by the emptiers 91 %.

intoponds

Week Total no.of tripsper week

No. oftripsresidentialareas

No. oftrips fromindustrialareas

Name ofindustry

1 139 111 28 KIUTA andRajani

2 143 126 17 KIUTA andRaj ani

3 137 113 24 ALAF, KIUTAand LeylandPaints

4 81 76 5 Rajani

5 125 125 0

6 140 136 4 Chandaria

7 71 71 0

8 160 150 10 Chandaria

Average no. ofMaximum “ ~1

45

The industrial wastewater carried by truck emptiers isbrought to the ponds periodically, that is once after acouple of days. This implies that the industries concerneddrain their wastewater into pits or underground tankswhere It is stored for some days before it is taken to thepond site.

The average number of trips per day is 26. More than 90 %of the wastewater brought to the pond site in truckemptiers is domestic. According to the interviewed truckoperators, the domestic wastewater brought to the pondswas collected from different parts of Dar es Salaam cityincluding areas beyond Temeke district. Howard Humphreys(1988) reported that the anaerobic ponds at Vingungutiwere designed to treat domestic wastewater from Temekedistrict alone. This practice, which was a result ofcbosure of some other pond systems in the city, may leadto suspect hydraulic overboading of the ponds.

puestionnaires

According to the questionnaires distributed to the variousindustries (Appendix 3) along Pugu Road, the informationcollected from the operators of truck emptiers anddiscussion with the authorities of the Dar es SalaamSewerage and Sanitation Department (DSSD), 20 industriesare reported to discharge their effluents into Vingungutiwaste stabilizat:ion ponds (Table 13). However, the figuremay be slightly lower than the actual because there arestil]. some unknown industries that use truck emptiers todeliver illegaLLy their wastewaters to Vingunguti pondsite.

46

Table 13. Industrial wastewater sources and pollutantsdischarged into Vingunguti ponds.

Tropical Foods

Steelwool

Paper Products

Diamond Motors

Pattex Knitwear

CALICO TextileIndustry

SADOLINS

TAZARA workshop

TANITA

YUASA battery

ALAF

Galaxy Paints

Leyland Paints

Rajani Oil

KIUTA

Incar (T)

Chandaria

Type of production/activity

production of vehiclesprings

fruit canning and

bottling

production of steelwool

printing

maintenance of vehicles

and sales of spare parts

production of textile

material

production of textile

material

production of paints

maintenance of auto-mobiles

cashewnut processing

manufacturing batteries

manufacturing corrugatediron sheets, asbestossheets and galvanizedpipes

production of paints

production of paints

production of cookingoi 1

paper binding/printing

maintenance of vehiclesand sales of spare parts

manufacturing pLasticbotties and toilet paper

pickling of steel sheets

and sales

laboratory works

Industry

TASIA

Major pollutants

oil, domesticwastewater

high organic wastes,

sugar and oil

domestic wastewater

colour, suspended solids

grease, oil and domestic

sewage

colour, suspended solids

colour, suspended solids

oils, colour

oil, grease and domesticwastewater

oil, suspended solids

acids, lead, zinc

toxic metals, heavy

metals

oils, colour

alkalis, colour, oil

oils

colour, suspended solids

grease, oil

suspended solids,domestic waste

acids, oil, domesticwastewater

acids, suspended solids

Wastewaterdisposal

sewer

sewer

sewer

sewer

sewer

sewer

sewer

sewer

sewer

sewer

sewer

truck

sewer

truck

truck

truck

truck

truck

truck

truck

Tanzania Auto-parts

NationalDistilleries

47

There are two categories of industries dischargingeffiuents into Vingunguti ponds:

1 those disposing wastewater through a sewer systemdirectly to Vingunguti ponds

2 those draining wastewater into pits located within theindustrial premises. The wastewater is then collectedby truck emptiers from the pits and transported toVingunguti ponds.

The effluents from the industries have been categorizedinto three groups:

1 Effluents consisting of biodegradabie organic material.Effluents from food processing industries andindustries producing seed er vegetable oils fall underthis category. These industries inciude TropicalFoods, TANITA and Rajani 0±1. Other industries likeSteel Wool (‘r) Limited and Chandaria do not use waterin their processes. The wastewater generated by suchindustries is almost domestic, coming from canteens andtoilets. This type of wastewater can easily be treatedin waste stabilization ponds.

2 Effluents containing grease and oil. Industries dealingwith maintenance of automobiles such as TAZARAworkshop, Incar (T) Limited, Diamond Motors and TASIAproduce this type of effiuents. Grease and oil af fectthe performance of ponds, especially facultative andmaturation ponds.

3 Toxic effiuents containing substances like heavy metals(lead, zinc, copper, etc), acids and dyes. Industriesproducing this type of effluents include textiieindustries such as CALICO Textile Mili and PattexKnitwear; pr:Lnting industries like Paper Products andKIUTA; paints industries such as SADOLINS, GalaxyPaints and Leyland Paints; metal industries like Alafand Tanzania Autoparts; and industries dealing withchemicals such as YUASA Battery and NationalDistilleries. Toxic substances inhibit the biobogicalgrowth in ponds and hence their presence is a problemthat cannot be overcome in the operation of pondsystems.

5.2.2 Biochemical oxygen demand

Biochemical oxygen demand (BOD5) measures the total amountof oxygen required to sustain biological activity in apond. The BOD5 reduction is generally the factor used fordesigning anaerobic and facultative ponds.

The values of BOD5 at Vingunguti waste stabilization pondsduring November ‘1991 - January 1992 are given In Table 14and Appendix 4.

48

Table 14. BOD5 values at Vingunguti waste stabilizationponds (November 1991 - January 1992).

Sample point BOD5

mean min maxmg/l mg/l mg/l

Al 186 160 210A0 173 140 2201 221 200 250FM1 135 100 160M1M2 121 110 130M2M3 123 110 1400 107 80 140

According to Arthur (1983), raw domestic wastewater inAfrican countries usualby contains 350 mg BOD5/l. Thisfigure is different. from the mean value of 186 mg BOD5/lfor the raw wastewater samples collected from the truckemptiers believed to carry more than 90 % domesticwastewater. Mogensen and Lunddal (1991), however, obtaineda mean value of 109 mg BOD5/b for the raw wastewatertreated in Lugalo waste stabilization ponds. This value iseven bower especially when it is considered that Lugaloponds are receiving onby domestic wastewater. Data fromvarious waste stabilization ponds in Dar es Salaam showvalues of BOD5 of raw domestic wastewaters ranging120 - 220. Suki et al (1988) have reported average valueof 137 mg/l and maximum value of 188 mg/l for BOD5 of rawdomestic wastewater from residential areas in KualaLumpur, Malaysia.

The BOD5 effluent value of 107 mg/l was higher than thatrecommended by the Tanzania Temporary Standards (TTS) foreffluents that are directly discharged into receivingwater bodies (30 mg/l). There are different opinions enthe subject of algae and their effect en BOD values. Varmaet al (1963) cited by Mogensen and Lunddal (1991) notedthat when algae die, being organic material, begin todecay and hence inc:rease the BOD of the sampie. The highconcentration of aigae observed in the maturation pondsmight have similarly af fected the effluent BOD5 resuitsobtained.

From Table 15, the BOD5 removal percentages in ponds A, F,M1, M2 and M3 were 7 %, 39 %, 20 %, —2 % and 13 %respectively. Total BOD5 removal was 48 %. Anaerobic pondsare not expected to have BOD5 removal efficiency below60 % for design temperatures >20 °C (Mara and Monte 1990).According to Howard Humphreys (1988), the Vingungutianaerobic ponds were designed for BOD5 removal of 70 %.

The strong smell coming out from the anaerobic ponds mayalso lead to suspect that the ponds are not performingwell. Objectionabie smeil is normally caused byoverloading of ponds and hence reducing the retention timeor by the presence of toxic substances in the influent(WHO 1987). The retention time can as well be reduced whenthere is excessive accumulation of sludge causing thereduction of the pond volume. The peer performance of the

49

anaerobic ponds may also be due to short—circuiting sincethe inlet pipes to the ponds were well above the surf acewater levels of the ponds. The raw wastewater may not bepassing through all the expected purification processes inthe ponds.

Table 15. Efficiency of each pond unit and totaleffic:Lency of Vingunguti waste stabilizationponds in the removal of various parametersduring November 1991 - January 1992.

Parameter Unit A F Ml M2 M3 Total

BOD5 % 7 39 20 —2 13 48NH3—N % —3 4 7 11 3 19FC % 4 93 62 57 77 99FS % 20 85 66 67 75 99TDS % 47 —7 17 0 —1 44NO3—N % 7 17 —5 0 13 20NO2—N % 17 47 23 —3 33 51Cu % 50 — — — — 68Cr % —68 — — — — —15

Note: 1. Mean concentrations were used in calculating thépercentage removals. All values that deviatedabnormally from other values were omitted(marked in brackets in Appendix 1).

2. The influent concentrations entering pond M1were calculated as the sum of the flow—weightedaverage concentrations coming from anaerobic andfacultative ponds through points AO and FM1respectively.

Mest of the samples taken directly from the truck emptierscontained some pesticides. Residents were said to beputting pesticides (such as DDT) in their pit latrines orseptic tanks to eradicate the streng odour of the sewagein their premises and also to inhibit mosquito breeding.Pesticides are highly toxic already in very smallconcentrations.

Values for removal of BOD5 for typical domestic sewage infacultative ponds is 70 - 90 % (Arceivala 1989). Theefficiency of the facultative pond at Vingunguti in theremoval of BOD5 was 39 %. This bow removal may beattributed to the fact that the facultative pond wasreceiving wastewater directly from industries. Thepresence of toxic substances accompanying industrialwastewater causes the die-of f of microorganisms hencereducing the BOD removal efficiency of the facultativepond.

Maturation ponds are mainly designed for reducingpathogenic organisms, therefore their peer performance inthe removal of BOD5 can be accepted.

50

5.2.3 Fecal coliforms and fecal streptococci

Fecal coliform (FC) and fecal streptococci (FS) tests areboth applied to indi.cate fecal contamination of water andwastewater (Feachem et al 1983). In this study, the testswere done to indicatte the pathogenic bacteria removal inthe pond system. Table 16 shows the calculated meanvalues of FC and FS counts which are also presentedgraphically in Figure 15.

Table 16. Mean, minimum and maximum values of FC and F5counts at. Vingunguti waste stabilization pondsduring November 1991 - January 1992.

Samplepoint

FC(counts/100 ml x i0~)

FS(counts/100 ml x 10~)

mean min max mean min max

Al 600 240 1670 1548 370 6600AO 575 85 1070 1232 210 39501 1232 120 1970 1840 910 3500FM1 87 4 301 280 32 1470M1M2 115 8 366 243 18 1060M2M3 49 3 102 80 21 1810 12 2 38 20 5 39

1500

1000

500

0

FC and ES

2000 (counts/100 ml x 1000)

,~ ‘t,

/ ‘t.

—t’— t

t.

t.t.

t.t

t

t

t

Al AD

‘F8

FC

Sampling points

01 FM1 M1M2 M2M3

Figure 15. Mean values of FC and FS counts at Vingungutiwaste stabilization ponds during November 1991- January 1992.

51

The identical pattern of FC and FS reduction rate shown inFigure 15 by the two different curves indicates that theresults can be relied en.

Mara (1977) cited by Mogensen and Lunddal (1991) suggestedthat for the purpose of designing stabilization ponds, avalue of 1 x 108 counts/100 ml FC be used for raw domesticsewage. A value of 0.4 x 108 FC counts/100 ml was used forthe design of Vingunguti ponds. Both these values areabove the value of 0.006 x 108 counts/100 ml observed enthe raw domestic wastewater discharged into the Vingungutiponds.

The limit recommended by the TTS for effluents from ponds(5 x 10~ counts/i00 ml FC) has been surpassed. The finaleffluent contains 11.5 x i0~ counts/100 ml FC. No mentionhas been made of the effluent standards for FS.

From table 15, the percentage removal of FC for ponds A,F, M1, M2, and M~) were calculated as 4 %, 93 %, 62 %, 57 %and 77 % respectively. The ability of anaerobic ponds toremove FC is usually insignificant. Very high removal ofFC and FS found in the facultative pond which have alsobeen indicated by sharp decline of the two curves inFigure 15, may not be due to the normal operation of thepond itself. It may be attributed to the presence oftoxic substances from industries which kill mest of themicroorganisms :Ln the pond including the pathogenicbacteria.

Fecal coliform reduction in each maturation pond (ranging57 - 77 %) averaged less than 90 % theoretical reductioncalculated by Marais (1974). The bower rates of die-of f ofpathogens in the individual maturation ponds at Vingungutimay be due to the high concentration of BOD5 in the ponds.Gameson and Saxon (1967) cited by Moeller and Calkins(1980) have reported that algae, as suspended solids,hinder the penetration of solar radiation, thus reduce theefficiency of ponds in destroying fecal coliforms. Theynoted that a filtered sample exposed to sunlight resultedin coliform destruction up to seven times that ofunfiltered sample.

The individual performance of the maturation ponds atVingunguti with fecal coliform reduction of 57 - 77 % was,however, similar to that of the West Hickman Creekwastewater lagoons in Kentucky, USA which showed meanreduction of fecal coliform ranging 62.9 - 77.4 % (Moellerand Calkins 1980J~.

During examining the bacteriological quality of the WestHickman Creek wastewater lagoons in Kentucky, USA.,Moeller and Calkins (1980) noted that coliform densitiesin the final three maturation ponds exhibited a distinctparallelism throughout the sample period. That is anincrease in coliform density from one sample date to thenext in the first pond was usually accompanied by a risein the second and third ponds. Similarly, a decrease incoliform concentration in the first pond was usuallyindicative of a decrease in the final ponds. A similar

52

trend was observed en the facultative pond (F) and the twomaturation ponds (M1 and M2) at Vingunguti (Figure 16).The concentrations of fecal coliforms in the effluentsfrom the last maturation pond M3 were toe small to beplotted en the graph.

120

100

80

GO

40

20

0

Sampling days

Figure 16. Fecal c:oliform densities in the facultativepond (F) and maturation ponds (M1 and M2)during November 1991 - January 1992.

5.2.4 Total dissolved solids

Table 17 shows the TDS values measured at Vingunguti wastestabilization ponds during the study. The graphicalpresentation of the values is given in Appendix 4.

Table 17. Mean, minimum and maximum values of TDS atVingungut:i ponds during November 1991 - January1992.

Sample points

mean

TDS

min maxmg/l mg/l mg/l

Al 1202 347 6390AO 642 320 11501 320 220 436FM1 343 260 460M1M2 397 350 480M2M3 397 347 4800 400 330 483

FC (counts/100 ml x 1000)

1 2 3 4 5 6 7 8 9 10

M2M3

M1M2

FM1

53

The effluent standard for TDS is 3 000 mg/l. The measuredeffluent TDS value of 400 mg/l indicates that theperformance of Vingunguti ponds has met the effluentrequirements recommended by the TTS. Table 15 shows thatthe anaerobic ponds have removed TDS contents by 47 %.According to this study, anaerobic ponds were the onlypond units where TDS were removed significantly. This maybe due to the sedimentation process that takes place inthe anaerobic ponds. In the facultative and lastmaturation ponds, TDS contents have shown te increaseslightly (1 - 7 % increase). This might be a result of thesuspended algae that grow in the facultative andmaturation ponds. The shallow depth of the maturationponds may also cause the detection of high TDS values dueto easy mixing of the settled particles by wind action.

5.2.5 Animonia, iiitrate and nitrite

Anunonia (NH3~jfl..

The amnionia concentrations are given in Table 18 andAppendix 4. The effluent requirement for ammoniareconunended by TTS is 10 mg/l N. The Vingunguti pondsystem has shown to meet this requirement as the effluentammonia content was 7.0 mg/l N.

Table 18. Mean, minimum and maximum concentrations ofaiumonia at Vingunguti. waste stabilization pondsduring November 1991 - January 1992.

Sample point

mean

NH3-N

min maxmg/l mg/l mg/l

Al 9.8 7.0 17.8AO 10.1 5.0 20.01 8.0 3.9 13.4FM1 7.7 1.2 12.6M1M2 8.2 0.5 12.0M2M3 7.3 0.3 14.00 7.1 0.5 12.6

The quality of the effluents from Vingunguti ponds withrespect to nitrate and nitrite concentrations wasrelatively better than of many operating ponds. Batcheboret al (1991) reported typical effluent concentrations ofnitrate and nil:rite from waste stabilization ponds as15.7 mg NO3-N/l and 0.3 mg NO2-N/l respectively. Theeffluent concentrations of nitrate and nitrite fromVingunguti waste stabilization ponds were 7.3 mg N03-N/land 0.4 mg N02-N/l respectively. This may be due to bowinfluent concentrations of the nitrogen compoundsexperienced by the ponds.

54

Table 15 shows that the percentage removal of ammonia inponds A, F, M1, M2 and M3 were -3 %, 4 %, 7 %, 11 % and3 % respectively. The total reduction of ammenia throughthe Vingunguti pond system was 19 %. This total removalefficiency is lower than anticipated. Removal efficienciesof anunonia in waste stabilizatien ponds have been reportedup to 99 % during sunimer with a minimum value of 90 %during winter in CaLifornia (USEPA 1983).

The removal of ammonia in ponds is carried out through thenitrification precesses. These precesses, like all otherbiological precesses, are sensitive to the presence oftoxic compounds including some heavy metals found inindustrial wastewaters. The ammonia removal efficiency ofthe Vingunguti ponds may have been af fected by thepresence of chromium in the wastewater. Beg et al (1980)found out that under shock bad condition, chromium has asignificant degree of Inhibition to nitrification process(even higher than arsenic er fluoride), thus af fecting theremoval efficiency of ammonia in a biological treatmentplant. However, the effect of the same toxicant over along period of time may not be the same as under shockbad conditions.

5.2.6 Heavy metals

The heavy metals tested were nickel, lead, cadmium, copperand chromium. Tests for cadmium, nickel and lead werestopped after performing for two days and find no tracesof the metals. Copper and chromium were tested for ninedays during the study. The reliability of the resuits ofthe heavy metal tests (Appendix 1) is, therefore, bow.

Heavy metals like nickel, lead and cadmium are usuallyproduced by such industries like metal industry andbattery industry. Their concentrations at the Vingungutiwaste stabilization ponds may have been toe low to bedetected by the ava:Llable equipments.

5.2.7 Dissolved oxygen, temperature and pH

Due to lack of proper equipment for measuring dissolvedoxygen (DO) levels and water temperatures (T) abong thepond depth, as recornniended by Pearsen et al (1987), theseparameters were measured en the upper water levels only.The measurements were, however, taken after samplingperiod was over as the dissolved oxygen meter for fieldmeasurements was not available at the beginning. Theresults (Table 19), therefore, cannot be directlycorrelated with the laboratory analyzes results obtainedearlier.

55

Table 19. Disse:Lved oxygen (DO) and temperature (T)measurements at Vingunguti waste stabilizationpends (10.— 14.2.1992).

Date Dissolved oxygen and temperature

A0 1 FM1 M1M2 M2M3

DOmg/l

T°C

DOmg/l

T°C

DOmg/l

T°C

DOing/1

T°C

DOmg/l

T°C

10.2.199211.2.199212.2.199213.2.199214.2.1992

7.84.85.23.66.4

24.022.021.521.521.5

6.05.84.42.24.8

22.522.522.522.022.0

11.88.8

12.49.4

12.0

23.022.021.521.522.0

10.66.67.66.07.2

23.522.021.022.022.0

11.010.0

7.87.57.8

22.022.021.021.021.0

Average 5.6 22.1 4.6 22.3 12.0 22.0 7.6 22.1 8.8 21.4

The raw industz-ial wastewater that enters into thefacultative pond had the bowest average DO content(4.6 mg/b). The most interesting observation was that thefacultative pond effluents, however, possessed the highestaverage DO content in the pond system (12.0 mg/l). Thismay be mainly due to the algal photosynthetic processestaking place in the facultative pond which caused the DOcontent of the industrial wastewater to raisetremendously.

Effluents from the first maturation pond had lower averageDO content (7.6 ing!].) than that of the effluents from thefacultative pond (12.0 mg/l). This was because, inaddition to the facultative pond effluents, the firstmaturation pond receives also anaerobic pond effluentswhich had bower average DO content (5.6 mg/l). With theexception of the values at the outlet of the facultativepond, the remaining values of DO content generallyindicate the anticipated trend of increasing DO content asthe purificatien process proceeds. The higher values of DOdewnstream are due to oxygen added through algalphotosynthetic activity. This is also signified by theincrease in pH dcwnstream (Oswald 1991).

It was not possible to measure the DO content of the finaleffluents from the pond system for the whole week. Due tosome rains that were falling during this period, there wasa mixture of pond water and stream water at the outlet ofthe last maturation pond and the readings obtained werenot bogical.

The average pond water temperature (at the surf ace) was21.9 °C. The raw industrial wastewater showed to haveslightly higher average temperature (22.3 °C).

56

pH measurement was done in the laboratory. Average pHvalues at Vingunguti waste stabilization ponds ranged7.3 - 8.3 (Appendices 1 and 4), the higher values being atthe downstream of the pond system. Zimba (1986) hasreported pH values ranging between 6 - 9 for selected pondsystems in Zambia, the effluent pH values being similarlyhigher than the influent values. The higher average valueof pH recorded at Vingunguti ponds (8.3) was bebow therequired for eptimum destruction of pathogens. Oswald(1991) reported that a pH of 9.2 for 24 hours will providea 100 % kil]. of E. Coli and presumably most pathogenicbacteria.

5.2.8 Flow measurement

Measurement of fbow were done using 900 V—notch weirs madeof steel (Figure 17).

A 90° V-notch weir installed at Vingungutiwaste stabilization pends.

Calibratiori of the weirs was done at site: a bucket of11.5 1 was filbed with pond effluent at the downstreamside of each weir. The time to fili the bucket at everyweir was recorded f ive times. Correspending water headmeasurements (h) at the V-notches were also recorded.Actual discharges 1:hrough the weirs were calculated fromthe volume of the bucket and the time durations recorded.

Figure 17.

4

57

Theoretical discharges were determined from the water headmeasurements (h) using the formula (Lindford 1981):

8Q = — (2.g)~ tan (v/2)~h5/2 (25)

15

where Q = theoretical discharge (m3/s)h = water depth over the V-notch (m)g = gravitational acceleration (9.81 m/s2)v V-notch angle (90°).

The coefficient of discharge (Cd) was determined as:

actual dischargeCd -

theoreticati. discharge

The resulting average coefficient of discharge for all theweirs was 0.5.

Discharges through the V-notches were, therefore,calculated from the observed water heads (h) usingequation (25) muitiplied by this factor (0.5).

The weirs were installed at points A0, FM1, M12 , M2M3 and

0. Influent flow into anaerobic ponds was estimated fromthe average number of truck emptiers that reported at thepond site daily. The capacity of one truck emptier was7 000 1. Industrial wastewater inflow into the facultativepond was estimated using a current-meter for one day.

Leakage around the edges of the V-notches was wellprevented using streng cement mortar but it was notpossible to seal the cracks in some channel walls whichlet the wastewater by-pass the V-notches especially atpoint M1M2. Water head readings at the V-notch weirs weretaken between 9.00 am and 4.30 pm, three times daily(Table 20).

58

Table 20. Discharge measurements at Vingungutistabilization ponds (10. — 14.2.1992).

waste

Date Time Discharge

AO1/s

FM11/s

M1M21/s

M2M31/s

10.2.1992 9.301.003.30

anipmpm

1.182.342.00

4.224.223.74

5.895.304.74

5.304.964.22

11.2.1992 9.401.403.30

ampmpm

4.023.122.71

2.561.941.82

3.743.292.42

3.372.872.14

12.2.1992 9.3011.15

2.30

amampm

0.961.181.09

2.142.341.53

3.742.871.82

3.742.711.70

13.2.1992 9.4000.30

3.44

ampmpm

1.000.731.27

1.761.421.27

2.141.421.27

1.941.371.22

14.2.1992 9.572.104.20

ampmpm

1.182.422.34

1.821.531.53

2.492.642.56

2.142.562.42

AverageMinimumMaximum

1.840.334.02

2.261.274.22

3.091.275.89

2.721.225.30

It was not possible to take readings at the outlet of thelast maturation pond (point 0). The weir installed at thispoint was damaged by a collapsing wall of the outletchannel. As the wall was leaning against the weir, theweir got deformed and it was unsafe to werk near theplace.

Table 20 shows that the inlet flow was always greater thanthe eutlet fbew for each pond unit. This loss was due toleakage through cracks en the channel walls, seepagethrough the bottoni of the ponds and evaporation. Thepercentage difference between inflow and outfiow for pondsA, M1 and M2 were 13 %, 24 % and 12 % respectively. Arelatively larger fraction of effluent from pond M1 (24 %)was not passing through the installed V-notch weir. Thiswas due to the large cracks found at the outlet channel ofthis pond causing the pond effluent to by-pass the weir.The average loss of wastewater in each pond due toevaporation and seepage can be estimated frem theanaerobic ponds and the second maturation pond te be12.5 %.

It is most likely that evaporation and seepage have takena significant volume of the pond waters causing infbow tobe greater than outflow. This is because the study period

t

59

coincided with the hottest and dryest season of the year(November - January) and also because the pond bottom wasunlined. Table 21 shows the montly temperature andrainfall recorded at the University of Dar es Salaammeteorobogical station during the sampling period.

Table 21. Month.Ly temperature and rainf all duringNovemJber 1991, December 1991 and January 1992(University of Dar es Salaani meteorologicalstation 1992).

Month Air temperature Averagerainf all

max min mean°C °C °C mm

November 1991 31.5 11.6 21.6 5.3December 1991 30.8 12.0 21.4 4.2January 1992 30.7 13.3 22.0 0.6

The measured fbows (Table 20) were smaller than the designflows. This may be because the design flows were projected20 years ahead (from 1988). Therefore the ponds are newworking under capacity (hydraulically).

5.2.9 Applicability of design equations

Anaerobic pond design eguatipns

The actual surface boading into the Vingunguti anaerobicponds based en the actual values of influent BOD5 andaverage infbow rate, was 850 kg/ha~d. Anaerobic ponds arerequired to have surface loadings more than 1 000 kg/had.This shows that the previded surface area of the ponds wasslightly (about 1.2 times) larger than required. However,surface boading is not recommended for use in sizinganaerobic ponds (Gboyna 1971 cited by WHO1987).

The volumetric loading into the Vingunguti anaerobic pondscalculated with equation (10) based on the actual valuesof influent BOD5 and infiow rates was 28 g/m

3’d. Thedesign voluinetr:Lc boading for temperatures >20 °C is300 g/m3.d (Mara and Monte 1990). This indicates that thevolume of the anaerobic pends is about 10 times greaterthan required using the volumetric boading rate designmethod.

The Vingunguti anaerobic ponds were designed with theretention time inethed (equation 11). The design flow was240 in3/d and the retention time was selected as 5 daysresulting in a total volume of 1200 m3. With the actualaverage flow of 182 m3/d, the corresponding retention timeduring the study was 6.6 days indicating that the pondswere operating fairly bebow their capacity. However,

60

according to Mara (1976 cited by WHO1987), BOD5 reductionshould have been >70 % for retention times >5 days. TheBOD5 reduction at the Vingunguti anaerobic ponds was only7 %.

Facultative ~end design eguations

Applying the Marais and Shaw first order reaction equation(18) with the actual values of influent and effluent BOD5and retention time, the resulting breakdown rate constant(kT) was 0.0114 d

1. The value of kT calculated withequation (19) and taking the average temperature as21.9 °C was 0.33 d~. The lower kT value reflec�s thelower rate of removal of organic material in thefacultative pond.

The bacterial die-of f constant (k~,J..

Table 22 gives the actual values of kb calculated from thekinetic equation (22) based on the actual retention timesof the pond units and actual average influent and effluentfecal celiform counts at Vingunguti ponds.

Table 22. Actual values of kb at Vingunguti wastestabilization ponds (11.11.1991 — 9.1.1992).

Pond unit Retentiontimed

kb

d~

A 6.6 0.007F 56.2 0.234M

1 37.7 0.044M2 56.8 0.024M3 60.3 0.054

The kb values for the three maturation ponds were notexactly equal, but were closer to be constant than thesefor the facultative and anaerobic ponds. The rate of fecalcoliform die-of f in the maturation ponds, therefore,closely obeyed the kinetic theory. The highest rate offecal coliferm die-•off in the facultative pond has beenreflected by the highest value of kb in the pond system.In the normal checking of pathogenic bacteria removal inwaste stabilization ponds using eguation (23), kb is takenas constant for all types of ponds (anaerobic, facultativeand maturation). This may not be correct as demonstratedby the variation of kb values en Tabbe 22. The reductionmechanisms in the three types of ponds are different.

Applying equation (24) and taking the pond watertemperature as 21.9 °C, the value of kb is 2.96 d’~. Thisvalue is far different from the values calculated inTable 22.

61

6 CONCLUSIONSAND RECOMMENDATIONS

6.1 Conciusions

The quality of effluents from the Vingunguti wastestabilization ponds do not comply with the requirements ofthe Tanzania temporary standards. This is concluded fromthe higher concentrations (than the standards) of the mostimportant parameters - BOD5 and FC - observed in the finaleffluents from the ponds. Effluent BOD5 and FC were107 mg/l and 11 500 counts/100 ml respectively whereas thestandard requires 30 mg/1 BOD5 and 5 000 FC counts/100 ml.

The concentrat:Lons of NH3-N, N03-N, NO2-N and TDS(7.1 mg/l, 7.3 mg/l, 0.4 mg/1 and 300 mg/1 respectively)have met the effluent standard requirements, but this maybe mainly because the concentrations of the parameters inthe raw wastewater received by the ponds were already low.

With the exception of pathogenic bacteria removal, theoverall treatment efficiency of the Vinguriguti wastestabilization pond system was poor. Overall efficienciesin the removal of BOD5, TDS and nitrogen compounds ranged19 - 51 %. FC and FS removal was above 98 %.

The individual performance of the anaerobic ponds was theworst with a BOD5 removal efficiency of 7 % only. Theanticipated BOD5 removal efficiency of an anaerobic pondis above 60 %. Ammonia was increasing by 3 % in the pondand nitrate and nitrite were removed by only 7 % and 17 %respectively. The anaerobic ponds have only been slightlyeffective in TDS removal (44 %) which, however, may beattributed to the sedimentation process in the pond andnot the biobegical activities of the microorganisms.

The cause of the total failure of the anaerobic ponds atVingunguti was not investigated in this study. It may bedue to sludge accumulation, short-circuiting, presence ofpesticides from pit latrines and septic tanks er toxicantsfrom industries that discharge wastewater illegally usingtruck emptiers.

The performance of the facultative pond was better thanthe anaerobic pends especially considering that thefacultative pond was treating purely industrialeffluents. BOD5 was removed by 39 % and FC and FS by 93 %and 85 % respect~Lvely. The high die-of f rate of pathogenicbacteria in the facultative pond is likely to be boostedby the toxicants from the industrial wastewaters. Theindustrial toxicants may, in contrast, be adverselyaffecting the reineval of BOD5 and the nitrogen compounds.

The three maturation ponds showed almost equal individualperformances in pathogenic bacteria removal with the lastpond (M3) being slightly the best. Their removalefficiencies ranging 57 - 77 % are common in mest welloperatirig maturation ponds.

62

Investigations en effluents from individual industriescould not be covered in this study. The few laboratorytests for copper and chromium done en samples collectedfrom the facultative pond inlet at Vingunguti showed thatthese metals were present. Cepper and chromium may beproduced by metal processing er battery manufacturingindustries. More heavy metals and ether toxic substancesfrom the textile, printing, paints and chemical industriesabong Pugu road are likely to be present in the Vingungutiponds.

In this study, it has also been observed that the BOD5 ofraw domestic wastewaters from pit latrines, septic tanksand even conventional sewerage systems in Dar es Salaammay be on the range 120 - 220 mg/1. The value of 350 mg/lBOD5 for raw demestic wastewater recemmended by manyauthors for design of waste stabilization ponds intropical areas may be teo high for the Dar es Salaamregion. Hewever, for designing pends to treat combinedwastewater, this value (350 mg/l) may be toe low, sinceeffluents of some irtdustries contain high BOD5.

The DO contents and pH values at the Vingunguti wastestabilization ponds were rising downstream indicating thatthe ponds were operating normally. The average pH valuesin the maturation ponds (ranging 7.7 - 8.3), which werebebow 9.0, preveci that the optimum destruction ofpathogenic bacteria was not achieved. -

6.2 Recoinmendations

Based en the findings of the study en the Vingunguti wastestabibizatien ponds the following is recommended:

1) Thoreugh investi.gatien en the complete failure of theVingunguti anaerobic ponds, in particular, sheuld becarried out. Investigation en the poor overallperformance of the Vingunguti pond system is alsoimportant. This should begin by focusing on thequabity and quarLtity of wastewater discharged by eachconcerned indust:ry.

2) A possibility to rearrange the wastewater flow at theVingunguti wast:e stabilizatien ponds to fellow thenermal order should be studied. That is, all the rawwastewater (domestic and industrial) should enter thepond system through the anaerobic ponds. From theanaerobic ponds, the wastewater should flow into thefacultative pond and finally into maturation pends.Anaerobic pends are important in pretreating varioustypes of industrial wastewaters.

3) The concerned industries should be encouraged topretreat their wastewaters te minimize the effects ofthe compounds irLhibitory to microbielogical activitiesin the ponds.

4) The crown levels of the raw wastewater inlet pipesentering the anaerobic and facultative ponds atVingunguti are required te be at a suf ficient depth

63

below pond water levels. This will enable easy mixingof the raw wastewater with the pond contents and henceavoid short-circuiting.

5) Simple and eifficient means of remeving algae from thefinal pond effluents is required to avoid secondarypollution to the Msimbazi river.

6) Maintenance and repair of the pond embankments andchannel walLs should be done whenever required toprevent further damage.

7) Flow, pH and temperature measurements at theVingunguti ponds should be recerded daily. Regularanalysis of important parameters, with emphasis enthose found :Ln industrial wastewaters, should be donefor better monitoring of the ponds performance. Thiswill help to make appropriate modifications tooptimize the performance of the pond system.

8) Almost all the existing formulas for design of wastestabilization ponds are principally based on theremoval of BOD and FC which are the cemmon pollutantsfound in domestic wastewaters. This is because,originally, waste stabilization ponds were meant fordomestic wastewater treatment. More studies should,therefore, be done en the effects of the varieusparameters found in different industrial wastewatersen the eperation of waste stabilizatien pends. Thiswill facilitate establishment of more proper methodsand formulas for designing waste stabilization pendsreceiving combined industrial and municipalwas tewaters.

64

7 REFERENCES

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Al-Salem, S.S. and Lumbers, J.P. 1987. An initialevaluation of Alsumra waste stabilization ponds (Jordan).Water Science and Technelogy. Vol. 19, no. 12, p. 33-37.

Arceivala, S.J. 1986. Wastewater treatment for pollutioncontrol. McGraw-Hil]. Publishing Company Ltd. p. 115-143.

Arellano, F. 1987. Pellution problems and control measuresfor the metal plating, alcohol, industrial chemicals andpaint manufacturing industries. Proceedings of thenational training course on industrial pollution controlfor small and medium scale industries, November 22—27,1987, Tagaytay, Phi].ippines. p. 48-49.

Arthur, J.P. 1983. Notes en the design and eperation ofwaste stabilization ponds in warm climates of developingcountries. World Bank Technical Paper no. 7. The WorldBank, Washington DC, USA. p. 7-61.

Banerji, S.K. and Ruess, B. 1987. Evabuation of wastestabilization pond performance in Missouri and Kansas,USA. Water Science and Technobogy. Vol. 19, no. 12,p. 39—46.

Batchelor, A., Bocarre, R. and Pylous, P.J. 1991. Low-costand low-energy wastewater treatment systems: A SouthAfrican perspective. Water Science and Technobogy.Vol. 24, no. 5, p. 241—246.

Beg, S.A., Siddiqi, R.H. and Ilias, S. 1980. Inhibition ofnitrification by arsenic, chromium and flouride. JournalWater Pollution Control Federation. Vol. 54, no. 5,p. 482—488.

Bramer, H.C. 1976. Water pollution control in the metalindustry. Industrial wastewater management handbook.McGraw-Hill Boek Company, New York. p. (9-1)-(9-55).

Diaz, A. 1987. Pollution problems and control measures forthe food industry. Proceedings of the natienal trainingcourse en industrial pollution control for small andmedium scale industries, November 22—27, Tagaytay,Philippines. p. 34-37.

Egbuniwe, N. 1982. Performance of a waste stabilizationpond treatment plant en a University campus. AfricanJournal of Science and Technology. Vol. 1, no. 1, p. 32-40.

Feachem, R.G., Bradley, D.J., Garelick, H. and Mara, D.D.1983. Sanitation and disease: health aspects of excretaand wastewater management. World Bank Studies in WaterSupply and Sanitation. John Wiley & Sons. 501 p.

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Gathuo, B. 1984. Industrial wastewater discharges withspecial reference to leather industry in Kenya. M.Sc.Thesis. Tampere University of Technology, Finland. p. 25-26.

Germirli, F., Tünay, 0. and Orhon, D. 1990. An everview ofthe textile industry in Turkey - pollution profiles andtreatability characteristics. Water Science andTechnobogy. Vol. 22, no. 9, p. 265-274.

Gilde, L.C. and Aly, O.M. 1976. Water pellution control inthe ood industry. Industrial wastewater managementhandbo k. McGraw-Hill Boek Company, New York.p. (5— )—(5—51).

Grau, P. 1991. Textile industry wastewater treatment.Water cience and Technology. Vol. 24, no. 1, p. 97-103.

Greenb rg, A.E., Trussell, R.R., Clesceri, L.S. andFranse , M.A. 1985. Standard methods for the examinationof water and wastewater. 16. edition. American PublicHealth Asseciation (APHA), Washington, USA. p. 373-917.

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Henze, M. 1983. Industrial wastewater treatment indeveboping countries. The Danish Açademy of TechnicalSciences, Lyngby,, Denmark. p. 20-27.

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Howard Humphreys (Tanzania) Ltd. 1988. Dar es Salaamsewerage and sanitation study — preliminary engineeringdesign and feasibility study. Final report. 508 p.

Karpe, H.J. and Baumann, W. 1980. Wastéwater treatment andexcreta disposa]. in developing ceuntries. Report en aresearch project by the Institute of EnvironnientalProtection (INFU), University of Dortmund, FederalRepublic of Germany. 121 p.

Linford, A. 1981. Flow measurement & meters. 5. edition.Lenghurst, S. and Turner, E. 1987. Combined treatment ofindustrial effluents. Industry and Environment, Vol. 10,no. 2, p. 11—16.

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Mara, D.D. and Monte, M.H.F. 1990. The design andoperation of waste stabilization ponds in tourist areas ofMediterranean Europe. Water Science and Technology. Vol.22, no. 3/4, p. 73—76.

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68

Appendix 1 (1/5)

Biochemical oxygen demand (BOD5) at Vingungutistabilization ponds (26.11.1991 — 16.1.1992).

*) Valuesvalues -

waste

1

Date Sampling points

Al A0 1 FM1 M1M2 M2M3 0

26.11.1991 190 150 220 100 120 110 10028.11.1991 160 (230)*)(140) 140 120 (160) 140

5.12.1991 (100) 140 250 100 120 (190) (180)10.12.1991 180 150 230 150 120 130 11017.12.1991 190 210 200 130 120 120 13019.12.1991 210 180 230 150 130 120 9026.12.1991 190 220 220 150 130 130 11031.12.1991 190 190 200 160 130 140 100

2.1.1992 (80) 160 (10) (60) (20) (20) (40)7.1.1992 (70) 140 (150) 110 120 110 809.1.1992 180 200 240 140 120 130 100

14.1.1992 200 190 210 130 120 130 10016.1 .1992 170 140 210 160 110 110 120

Average 186 173 221 135 121 123 107

*) Values in brackets omitted when calculating averagevalues.

Total disselved solids (TDS) at Vingunguti wastestabibization ponds (26.11.1991 — 16.1.1992).

Date Sampling points

Al AO 1 FM1 M1M2 M2M3 0

26.11.1991 400 460 415 370 350 360 44528.11.1991 347 360 436 320 442 480 415

3.12.1991 472 320 376 342 361 347 4835.12.1991 420 373 391 380 373 402 416

10.12.1991 417 361 387 420 375 416 36212.12.1991 465 375 355 460 370 420 38617.12.1991 380 (1020)*) 230 260 390 400 40019.12.1991 390 (1200) 230 280 410 400 42026.12.1991 2190 1100 300 290 360 370 34031.12.1991 410 365 380 370 368 390 401

2.1.1992 670 1100 310 310 360 390 3307.1.1992 4300 1090 270 330 390 400 4709.1.1992 6390 1150 220 330 460 410 (700)

14.1.1992 350 (1210) 250 330 480 400 36016.1.1992 430 (1200) 250 360 460 370 370

Average 1202 642 320 343 397 397 400

in brackets emitted when calculating average

69

Appendix 1 (2/5)

(FC) counts at Vingunguti11.1991 — 9.1.1992).

Date Fecal coliform (counts/100 ml) at point

Al AO 1 FM1 M1M2 M2M3 0

11.11.1991 350 85 — 116 269 38 1.813.11.1991 440 340 1265 104 296 23 2.226.11.1991 470 170 938 301 366 91 5.128.11.1991 420 940 1590 188 78 61 5.6

3.12.1991 490 160 1080 18 66 26 7.25.12.1991 — 1040 1920 98 78 97 19

10.12.1991 930 1070 1970 84 72 64 3812.12.1991 1670 970 1920 92 112 102 2317.12.1991 690 570 120 44 52 41 726.12.1991 540 970 1120 34 60 38 21.431.12.1991 640 990 1080 88 66 40 10

2.1.1992 530 180 600 22 48 34 12.47.1.1992 240 90 — 4 8 3 2.49.1.1992 390 480 1180 24 34 21 5.4

Average 600 575 1232 87 115 49 11.5

Fecal streptococci (FS) at Vingunguti waste stabilizationponds (11.11.1991 — 9.1.1992).

Date Fecal Streptecocci (counts/100 x i03 ml) at

Al AO 1 FM1 M1M2 M2M3 0

11.11.1991 6600 2725 — 1470 633 141 35.413.11.1991 4030 3950 3500 1030 1060 109 3926.11.1991 1970 1900 — 340 378 181 3528.11.1991 940 760 910 130 156 67 17

3.12.1991 410 320 — 66 128 22 12.25.12.1991 — 1610 1870 104 96 105 22

10.12.1991 1260 1630 1670 108 98 103 2612.12.1991 490 210 1980 254 376 96 5.417.12.1991 960 660 — 104 112 71 12.226.12.1991 600 780 1440 40 28 48 1831.12.1991 710 790 1610 49 30 50 17.5

2.1.1992 1370 980 2100 160 236 68 247.1.1992 370 240 — 32 18 21 9.69.1.1992 420 690 1480 32 54 34 7.8

Average 1548 1232 1840 280 243 80 20

Fecal coliformstabilization ponds (11.

waste

70

Appendix 1 (3/5)

Ammonia (NH3-N)stabilization ponds

concentration at Vingunguti(11.11.1991 — 16.1.1992).

waste

Date Ammonia concentration at point

Al AO 1 Fl41 M1M2 M2M3 0mg/1 N mg/1 N mg/1 N mg/1 N mg/1 N mg/1 N mg/1 N

11.11.1991 15.5 12.9 3.9 2.0 0.5 0.3 0.513.11.1991 17.8 18.3 5.5 1.2 0.8 1.0 1.226.11.1991 12.4 14.2 6.4 12.6 10.5 14.0 12.628.11 .1991 9.2 12.3 13.4 12.6 10.7 10.4 7.6

3.12.1991 10.0 20.0 10.0 10.0 12.0 8.0 10.05.12.1991 1LO 12.0 10.0 10.0 11.0 9.0 11.0

10.12.1991 (20.0)*) 14.3 (20.0) 10.5 (20.0) 10.0 (25.0)12.12.1991 7.0 6.0 7.0 9.5 9.0 6.5 6.517.12.1991 9.5 5.0 6.5 6.0 9.5 7.0 5.019.12.1991 8.0 7.5 8.0 6.0 9.0 6.8 6.026.12.1991 8.0 8.0 7.5 5.0 8.6 6.5 8.031.12.1991 9.0 12.0 12.5 9.5 9.0 7.0 7.0

2.1.1992 8.0 9.0 9.0 5.5 9.0 60 8.07.1.1992 8.0 5.0 7.5 7.0 6.6 7.0 6.09.1.1992 9.9 9.0 7.0 7.0 8.0 6.5 8.0

14.1.1992 7.5 7.0 7.0 8.0 9.0 9.0 9.016.1.1992 7.0 7.0 7.0 8.0 8.0 9.0 7.0

Average 9.8 10.1 8.0 7.7 8.2 7.3 7.1

*) Values in brackets omitted whenvalues.

Nitrite (N02-N) concentration atStabilization ponds (26.11.1991 - 9.1

*) Values in brackets emitted when

Vingunguti.1992).

Waste

calculating average

calculating average

Date Nitrite concentration at point

AO Al 1 FM1 M1M2 M2M3 0mg/1 N mg/1 N mg/1 N ing!]. N mg/1 N mg/]. N mg/1 N

26.11.1991 1.67 1.05 4.70 1.42 1.18 1.25 (3.28)*)28.11.1991 0.95 0.133 1.24 0.87 0.69 0.87 (1.13)

3.12.1991 1.00 0.90 2.10 0.80 0.70 0.70 0.5010.12.1991 1.05 1.25 1.50 1.20 1.50 1.50 1.2512.12.1991 0.25 0.20 0.20 0.20 0.35 0.40 0.3017.12.1991 0.60 0.20 0.20 0.20 0.60 0.50 0.2019.12.1991 0.40 0.30 0.20 0.20 0.50 0.40 0.2026.12.1991 0.40 0.30 0.30 0.20 0.30 0.30 0.2031.12.1991 0.60 0.80 0.40 0.30 0.40 0.40 0.30

2.1.1992 0.40 0.20 0.20 0.20 0.30 0.30 0.207.1.1992 0.32 0.30 0.20 0.20 0.20 0.30 0.209.1.1992 0.30 0.24 0.20 0.20 0.20 0.20 0.22

Average 0.66 0.55 0.95 0.50 0.58 0.60 0.40

values.

71

Appendix 1

Nitrate (N03-N) cencentration at Vingungutistabilization ponds (28.11.1991 — 16.1.1992).

(4/5)

waste

Date Nitrate concentration at point

Al A0 1 FM1 M1M2 M2M3 0mg/1 N mg/]. N mg/1 N mg/1 N mg/1 N Ing!]. N ing!]. N

28.11.1991 7.6 8.5 12.1 9.2 8.3 (11.3)*) 9.63.12.1991 10.5 10.5 10.5 8.5 7.8 6.9 6.0

10.12.1991 10.5 (20.0) (20.0) 10.0 8.5 10.5 10.012.12.1991 9.0 8.5 10.0 8.5 7.5 9.0 6.017.12.1991 9.8 6.8 9.5 8.0 10.0 9.5 6.019.12.1991 9.0 9.5 9.0 7.0 10.0 9.0 6.526.12.1991 9.0 8.5 9.0 7.6 9.0 10.0 6.031.12.1991 10.0 9.5 10.5 8.5 8.0 8.5 7.5

2.1.1992 9.0 8.0 9.0 7.0 9.0 9.0 7.07.1.1992 6.0 5.5 7.0 5.3 5.0 6.0 5.49.1.1992 9.0 8.0 7.8 7.6 9.0 6.0 (6.8)

14.1.1992 8.0 7.5 9.0 7.5 9.0 8.5 9.016.1.1992 8.0 7.0 9.0 7.0 8.0 8.0 9.0

Average 8.8 8.2 9.4 7.8 8.4 8.4 7.3

*) Values in brackets omitted whenvalues.

calculating average

Concentration of copper (Cu) atstabilization ponds (17.12.1991 — 16.1

Vingunguti.1992).

waste

Date Concentratien of Copper at point

Al AO 1 0mg/l mg/l mg/l mg/l

17.12.1991 1.00 (23.00)*) 9.00 1.0019.12.1991 0.06 0.12 0.01 0.2726.12.1991 0.80 0.10 0.01 0.1231.12.1991 0.10 0.10 0.20 0.10

2.1 .1992 0.50 0.10 0.05 0.197.1.1992 (4.00) (6.00) 0.03 1.009.1.1992 3.00 2.00 7.00 1.00

14.1.1992 0.06 0.02 0.05 0.0616.1.1992 0.07 0.04 0.08 0.06

Average 0.70 0.35 1.83 0.42

*) Valuesvalues.

in brackets omitted when calculating average

72

Appendix 1

Concentration of chremium (Cr) at Vingungutistabilizationponds (17.12.1991 — 16.1.1992).

(5/5)

was te

Date Concentration of chromium at peint

Almg/l

AOmg/l

1mg/1

0 -

mg/l

17.12.199119.12.199126.12.199131.12.1991

2.1.19927.1.19929.1.1992

14.1 .199216.1.1992

0.301.000.011.000.601.001.000.040.05

4.000.030.600.100.601.002.000.010.10

0.020.030.050.010.031.003.000.070.07

1.002.000.110.100.201.001.000.010.02

Average 0.56 0.94 0.48 0.60

pH values(11 .11 .1991

at Vingunguti— 16.1.1992).

waste s tab iii zat i on ponds

Date pH values at points

Al A0 1 Fl41 M1M2 M2M3 0

11.11.1991 7.5 7.6 6.9 8.1 8.2 9.1 8.813.11.1991 7.6 7.7 6.9 8.4 8.1 9.1 9.126.11 .1991 7.7 7.8 6.8 8.4 7.6 8.5 9.428.11 .1991 7.3 9.6 8.6. 7.8 7.5 8.9 8.2

3.12.1991 7.4 7.6 6.7 8.2 8.4 9.2 8.610.12.1991 8.7 9.6 9.0 8.2 7.6 8.3 8.612.12.1991 7.8 7.9 9.1 8.2 7.5 8.4 8.717.12.1991 7.4 7.6 7.2 8.0 7.6 7.8 9.019.12.1991 6.5 6.7 6.8 9.0 7.2 8.3 8.026.12.1991 6.8 6.9 6.7 8.5 6.6 7.7 7.831.12.1991 7.0 7.5 6.9 8.4 7.5 8.0 8.5

2.1 .1992 7.5 6.7 6.0 6.8 6.4 6.3 6.57.1 .1992 7.5 8.0 7.0 9.0 8.0 7.8 8.09.1 .1992 7.5 7.8 7.4 7.5 9.0 8.0 8.0

14.1 .1992 6.8 7.6 7.4 8.0 7.5 7.6 7.816.1.1992 6.8 7.5 6.5 8.5 8.0 8.0 7.6

Average 7.4 7.8 7.3 8.2 7.7 8.2 8.3

73

Appendix 2

Tanzania temporary standards for effluents meant fordirect discharge into receiving waters (Tanzania Bureau ofStandards 1988 cited by Howard Humphreys 1988).

Substance Unit Maximum permissiblevalue

BOD5TDS

mg/].mg/].

303000

FC no./100 ml 5000NH3-NN03-NNO2-NDO

mg/].mg/].mg/].mg/].

1050

1.05.0

pH - 6.5—8.5Pb mg/l 0.2Zn mg/l 1.0Cd mg/]. 0.1Cr mg/3. 0.1Cu mg/]. 0.1Ni mg/i. 0.2

74

Appendix 3

An example of a questionnaire sent to the industriescontributing wastewater to Vingunguti waste stabilizatienponds.

SURVEYOF INDUSTRIAI.I EFFLLJENTS - OUESTIONNAIRE

Name of coinpany:

Address or location::

Nuniber of shifts per day: 1

Work force per shif t: 65

Canteen facilities: Yes

Water sources:

Average water consull]ption:

Peak rate of consumption: — 1/s

Goods ma.nufactured 0E processed:

Canned and bottled food products

Processes employed in manufacture:

Raw material (fruits) ---> sorting ---> washing --->

sorting ---> juice extraction --- blending/mixing --->

filling ---> processing (applying temperature andpressure)

Volume of process water discharged to waste: 5 000 l/d

Peak rate of wastewater discharge: - 1/s

Future development plans including introduction of newprocesses: Extensions

Present treatment facilities: Nil

Present method of disposal of liquid waste:

Sewerage system that goes to Vingunguti wastestabilization ponds

General observations: Nil

Name and position olE persen interviewed:

Mr Robert Mkangila / Factory Engineer

Date: 27.11.1991

Tropical Foods Limited

Plot no. 12, Vingunguti,Pugu Road

Duration of shift: 8 h

National Urban Water Authority

20 m3/d

75

BODS (my/1)

Al AD

BOD5 at Vingunguti waste

26.11.1991 — 16.1.1992.

1500TD5 (mg/1)

1000 -

500

0

Appendix 4 (1/3)

TDS at Vingunquti waste stabilization ponds26.11.1991 — 16.1.1992.

150:.

100•1 FM1 M1M2 M2M3 0

Sampling point

stabilization pends during

Al A(J 1 FM1 M1M2 M2M3 0

Sampling point

during

Rmmonia (mg/1 N)

76

Appendix 4 (2/3)

:10.0 H9.5 -

9.0 H8.5 ~-

8.0 H7.57.0

H: 1 t t t t

Al AD 1 FM1 M1M2 M2M3 0

Sampling point

Concentratien of ammenia at Vingunguti waste stabilizationponds (26.11.1991 — 9.1.1992).

AD Al 1 FM1 M1M2 M2M3 0

Sampling points

Concentration of nitrate at Vingunguti waste stabilizationponds (26.11.1991 — 16.1.1992).

100Nitrate conc~ntration (mg”l N)

9.5

9.0

8.5

8.0

7.5

7.0

77

Nitrite concentratioh (mg/1 N)1.00

0.75 -

0.50

Sampling points

Appendix 4 (3/3)

Concentration of nitrite at Vingunguti waste stabibizationponds (26.11.1991 — 9.1.1992).

AD Al 1 FM1 M1N12 M2M3 0

3